Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites

Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites Ido Hadar, Amar Nath Yadav, Du Chen, Shunran Li, Mikaël Kepenekian, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7431342/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Understanding the effect of organic spacers on the fundamental excited-state processes in 2D perovskites is crucial for advancing these novel materials. Herein, we study these processes for manganese (Mn)-doped 2D Ruddlesden-Popper perovskites with aromatic phenethylammonium (PEA) and aliphatic butylammonium (BA) spacer ligands. Mn-doping offers a powerful strategy for tuning and enhancing the optoelectronic properties of halide perovskites. Despite notable advancements, the Mn-based emission dynamics and the spacer’s influence on the doping mechanism remain poorly understood. We explore Mn-doped 2D perovskites by varying the organic spacer and Mn molar fraction, examining nanoplatelets, and bulk crystals. We observe a complete substitution of Mn 2+ ions at the crystals’ edges at high doping levels, and a uniform distribution at lower ones, for both spacers. Yet, the Mn-emission differs significantly based on the spacer. PEA-based perovskites exhibit strong emission with a photoluminescence quantum yield of 75%, dropping to 57% for BA. To uncover this contrast, we probed exciton transport using transient reflection microscopy, revealing nearly twice the exciton diffusivity in PEA compared to BA. We further correlate crystal rigidity and exciton–phonon coupling with diffusivity. This work offers a general framework for studying spacer effects in 2D perovskites, guiding the design of advanced luminescent materials. Physical sciences/Chemistry/Materials chemistry/Optical materials Physical sciences/Materials science/Nanoscale materials/Structural properties Physical sciences/Nanoscience and technology/Nanoscale materials/Organic–inorganic nanostructures Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials 2D perovskites doping cathodoluminescence exciton–phonon coupling diffusivity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction In recent years, Ruddlesden-Popper (RP) series of two-dimensional (2D) layered perovskites have attracted significant attention due to their outstanding optoelectronic properties. 1 – 9 The RP perovskites are solution-processed quantum-well structure which can be formed by substituting the A-site cation in three-dimensional (3D) perovskites, ABX 3 ​(where A + = Cs, methylammonium (MA), formamidinium (FA); B 2+ = Pb, Sn; and X − = Cl, Br, I), with long-chain organic spacer ligand (L) such as butylammonium (BA), phenethylammonium (PEA), among others. 10 , 11 These structures are described by the chemical formula of L 2 A n − 1 Pb n X 3 n +1 , where n denotes the number of inorganic octahedral layers. 12 – 14 This series exhibits remarkable structural flexibility, enabling bandgap tunability, narrow absorption and photoluminescence (PL) spectra, high exciton binding energy, long charge-carrier diffusion lengths, and enhanced environmental stability imparted by the intercalated organic spacer ligands. 15 – 21 The single-layer 2D RP perovskites (L 2 PbBr 4 , n = 1) generally exhibit low PL quantum yield (PLQY) due to self-absorption processes and a high surface-to-volume ratio. 4 , 12 , 22 Doping or alloying with foreign metal ions (Cd 2+ , Zn 2+ , Mn 2+ , Sn 2+ , etc. ), has been explored as a strategy to enhance their PLQY and to tune their optoelectronic properties. 23 – 29 Among these metal ions, Mn 2+ doping has been extensively studied due to its unique dual emissions originating from the band edge (high-energy narrow emission) and Mn 2+ states (broad emission at lower energy). 15 , 25 , 30 – 35 The absence of self-absorption of dopant emission, along with efficient coupling between charge carriers and dopant ions, enables Mn 2+ based emission to achieve an exceptionally high PLQY of up to 97%. 36 These remarkable properties broaden the potential applications of these materials in solid-state lighting, X-ray scintillators, and luminescent solar concentrators. 15 , 37 , 38 While considerable advancements have been made in the synthesis and optimization of the optoelectronic properties of Mn-doped 2D RP perovskites, the fundamental understanding of the Mn 2+ doping mechanism and excited-state processes remains limited. For the doping mechanism, the exact sites of Mn 2+ ions (substitutional versus interstitial) in the inorganic framework remain a subject of extensive debate. Recently, Kuruppu et al. reported interstitial doping of Mn 2+ in (PEA) 2 PbBr 4 , whereas substitutional doping was observed in (BA) 2 PbBr 4 perovskites. 39 In contrast, Ba et al. and Gao et al. suggested that the substitutional nature of Mn 2+ doping is present in both PEA- and BA-based 2D perovskites. 33 , 40 ​Moreover, the role of spacer ligands in modulating Mn-based luminescence remains poorly understood. In a recent article, it was found that decreasing the chain length of spacer ligands leads to an increase in the PLQY of Mn-doped 2D RP perovskites. 41 Contrarily, the PLQY of 2D perovskites does not depend systematically on the ligand chain length but instead on the electron-phonon interaction. 42 – 44 Therefore, a detailed investigation by varying spacer ligands and Mn-doping levels is crucial to fill these gaps. In this study, we synthesize Mn-doped 2D RP perovskites in the form of nanoplatelets (NPLs) and bulk crystals, with the chemical formula of L 2 Pb 1 − x Mn x Br 4 , by varying the Mn molar concentration ( x ) and using aromatic or aliphatic amines as spacer ligands. Specifically, we select PEA from the aromatic amine series and BA from the aliphatic amine series of spacer ligands to investigate the correlation between the structural modifications and the optical properties of the Mn-doped 2D perovskites. While the choice of spacer ligand has a minor effect on the structure and emission of undoped 2D perovskites, our findings demonstrate that it plays a crucial role in modulating Mn 2+ -based emission. Strong dopant emission is observed when aromatic PEA is used as the spacer ligand, whereas the dopant emission is significantly lower when aliphatic BA is employed. Surprisingly, structural analysis reveals two doping mechanisms for high and low Mn concentrations. At low Mn doping, the dopants are uniformly distributed across the NPL area. However, for high Mn doping, a complete dopant substitution at the edges of the NPLs is observed, accompanied by the formation of a new phase, L 2 MnBr 4 . The formation of the new phase at higher doping is supported by high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and cathodoluminescence (CL) spectroscopy. These doping mechanisms (Mn 2+ replaces Pb 2+ sites) are observed for both PEA and BA structures in NPLs and bulk crystals. Based on the similarities in crystal structure, band-edge emission, and doping mechanisms, we concluded that the differences in Mn emission and PLQY between PEA- and BA-based 2D perovskites lie in the excited-state dynamics and carrier mobility. Therefore, we investigate the exciton transport properties of these perovskites using pump-probe transient reflection microscopy (TRM). 45 This advanced technique enables the direct extraction of exciton diffusivity values, revealing that PEA-based perovskites exhibit nearly twice the diffusivity of their BA-based counterparts, and as a consequence, much higher charge mobility. We attribute this enhancement in mobility to the more rigid crystal structure imparted by the aromatic spacer PEA, which weakens the exciton–phonon coupling strength. In contrast, the softer lattice associated with the BA spacer leads to stronger exciton–phonon coupling and consequently reduced mobility. The highly mobile excitons in PEA-based perovskites readily dissociate into free charge carriers, which are efficiently transferred to Mn 2+ sites, thereby enhancing the Mn 2+ emission. In contrast, charge transport is slower in the case of BA, resulting in weaker Mn 2+ emission. These observations suggest a general approach to studying charge mobility in halide perovskites, specifically its correlation with subtle changes in the crystal structure induced by the organic spacers. Results and Discussion Investigation of the light-emitting properties and precise location of Mn 2+ ions in Mn-doped 2D RP perovskites The colloidal undoped (L 2 PbBr 4 ) and Mn-doped 2D RP perovskite (L 2 Pb 1 − x Mn x Br 4 ) NPLs with varying Mn concentration x (where “ x” is defined as the Mn-mole fraction calculated from the precursor ratio Mn/(Mn + Pb)) are synthesized using the ligand-assisted reprecipitation (LARP) method, as described previously. 15 , 30 More details about synthesis can be found in the supporting information ( SI , section S1) . In this study, we utilize two different spacer ligands: an aromatic amine, PEA ((PEA) 2 Pb 1− x Mn x Br 4 ), and a linear aliphatic amine, BA ((BA) 2 Pb 1− x Mn x Br 4 ), with x varying from 0 to 1. The selection of these two spacers is based on their structural properties. PEA is an aromatic and rigid spacer with a bulky structure due to its phenyl ring, which promotes strong π–π interactions between adjacent ligands and results in a more ordered and stiffer 2D perovskite lattice. In contrast, BA is an aliphatic and flexible spacer with a linear alkyl chain, leading to greater lattice flexibility and increased structural disorder based solely on van der Waals interactions. 46 , 47 Despite these differences, both spacer ligands yield a series of 2D RP perovskites with similar structures and optical properties. 12 Figure 1 A-E represents a schematic of the structure, PL spectra, and color change under UV (365 nm) for the undoped and Mn-doped 2D RP perovskites (PEA versus BA). Figure 1 B and C show the changes in PL with varying x normalized by the band-edge emission (410 nm). The subsequent changes in the absorption spectra are depicted in Figure S1 . After doping with Mn, the NPLs exhibit band-edge emission and a broad emission centered at 610 nm, which corresponds to the characteristic optically forbidden 4 T 1 – 6 A 1 transition from the Mn 2+ d - d state. 15 , 30 , 34 As x varies from 0 to 0.70, a monotonic increase in the emission from the Mn 2+ state becomes evident for both PEA- and BA-based samples. In particular, two regimes are clearly observed from the PL spectra: for x ≤ 0.5, the emission from Mn 2+ states is weaker than the band-edge emission, whereas for x > 0.5, the Mn 2+ emission is significantly enhanced and dominates the band-edge emission for both PEA- and BA-based perovskites. Notably, PEA-based NPLs exhibit higher Mn 2+ emission compared to their BA-based counterparts, which can also be validated by the color changes of colloidal NPLs (dispersed in toluene) under UV illumination (365 nm) (insets of Figs. 1 B and C ). Both PEA- and BA-based undoped ( x = 0) NPLs show similar violet emission. Further, Mn-doped PEA-based NPLs show a color change from pink to orange as x varies from 0.25 to 0.50. In contrast, for BA-based doped NPLs, a similar transition is seen when x ranges from 0.50 to 0.70 (higher than PEA). This can also be supported by the changes in CIE color coordinates, which are plotted based on the PL spectra ( Figure S2 ). To further validate these results, we performed PLQY measurements using the direct integrating sphere method ( Figure S3 ). The undoped perovskites NPLs exhibit relatively low PLQY values of 8.0% and 6.7% for (BA) 2 PbBr 4 and (PEA) 2 PbBr 4 , respectively. Upon Mn doping, the PLQY of both perovskites increases remarkably. Specifically, PEA-based 2D perovskites show significantly higher PLQY values (12.5–75.0%) than the BA-based ones (8.5–57.0%) across the same range of Mn mole fractions ( x = 0.12–0.70). Here, most of the contribution to the total PLQY originates from the Mn 2+ emission peak rather than the band-edge. The substantial difference in Mn 2+ emission and PLQY between PEA- and BA-based perovskites could be attributed to three main factors: (1) differences in the actual doping percentage at the same nominal Mn concentration ( x ), (2) variation in the spatial incorporation of Mn 2+ ions, such as substitutional versus interstitial sites within the inorganic lead octahedral, and (3) structural differences imposed by the spacer ligands, leading to distinct excited-state charge carrier dynamics. In the following paragraphs, we will examine each of these three possibilities one by one. To determine the exact doping percentage of Mn in the 2D perovskite NPLs, we performed inductively coupled plasma mass spectrometry (ICP-MS), and the results are shown in Table S2-3 . When x (Mn feed ) varied from 0.12 to 0.70, the Mn atomic percentage (with respect to Pb) ranged from 2.49–47.05% for PEA-based NPLs and from 2.12–46.54% for BA-based NPLs. Here, a nonlinear trend between the Mn feed and actual doping level (Mn%) is evident, with the conversion yield for Mn 2+ ions being lower than that of Pb 2+ . 15,30 Interestingly, similar Mn doping percentages in both PEA- and BA-based NPLs suggest that the doping level is independent of the spacer ligands, which give rise to the same series of 2D RP perovskites. These findings strongly indicate that the choice of spacer ligands has a negligible effect on the actual Mn doping concentration. Next, we measured powder X-ray diffraction (XRD) patterns to monitor the structural changes induced by Mn 2+ doping. The XRD patterns for (PEA) 2 Pb 1− x Mn x Br 4 and (BA) 2 Pb 1− x Mn x Br 4 , ( x = 0, 0.25, 0.50, 0.70, and 1), are shown in Fig. 1 D and E , respectively. After careful observation, we notice an overall shift of the diffraction planes to large angles (smaller distances), in both PEA- and BA-based NPLs (right panel of Figs. 1 D and E) . This trend is typically observed in doped semiconductors resulting from substitutional doping. 48 In this case, substitutional doping by Mn 2+ at the Pb 2+ site in the octahedral slab leads to lattice contraction, as the six-coordinate crystal ionic radius of Mn 2+ (0.97 Å) is smaller than that of Pb 2+ (1.33 Å). 48 Additionally, it can be observed that the diffraction planes appear at regular intervals, indicating a layered structure. 4 The periodicities (Δθ) along the (00 l ) planes are found to be 5.35° and 6.50° for (PEA) 2 PbBr 4 and (BA) 2 PbBr 4 NPLs, respectively. These correspond to average distances of 1.6 nm (PEA) and 1.3 nm (BA) between adjacent lead octahedral layers, calculated using Bragg’s diffraction equation. Considering the similar size of a single lead octahedron (~ 0.6 nm) in both perovskites, the changes in the average distances between adjacent inorganic layers are attributed to the different sizes of the intercalated spacer ligands. The effective sizes of spacers are estimated to be larger for PEA (1 nm) than for BA (0.7 nm) ( Figure S4 ). 12 In addition, upon careful observation, a new series of planes also appears at regular intervals at higher doping levels ( x > 0.5). When we recorded the XRD patterns of L 2 MnBr 4 (L = PEA or BA, x = 1; shown at the top of Figs. 1 D and E ), the planes closely matched additional planes observed (highlighted in the figure) in L 2 Pb 1 − x Mn x Br 4 ( x = 0.70). This indicates that phase separation occurs between L 2 MnBr 4 and L 2 Pb 1 − x Mn x Br 4 when Mn 2+ ions are excessively doped ( x > 0.5). Similar types of structures, including (PEA) 2 MnBr 4 , (PEA) 2 MnCl 4 , CsMnCl 3 , etc. , have also been reported previously. 49 – 51 To find the size and shape morphology as well as the distribution of Mn across the NPLs, we performed EDS mapping using scanning transmission electron microscopy (STEM). Figure 2 A and B depict high-angle annular dark-field (HAADF)-STEM images and EDS mapping results for low ( x = 0.25) and high ( x = 0.60) doping of Mn in (PEA) 2 Pb 1−x Mn x Br 4 NPLs. The size of the NPLs ranges from 500 to 1000 nm, with a rectangular shape and rounded corners, maintaining their 2D structure (Fig. 2 ). The EDS mapping depicts that for the low doping levels the Mn atoms are uniformly distributed across the NPLs (Fig. 2 A). In contrast, at higher doping levels, the majority of the Mn atoms are concentrated along the edges of the NPLs, in addition to being distributed within the interior (Fig. 2 B). This result is well-consistent with the XRD findings and indicates that the phase separation observed in the XRD patterns occurs at the edges of the NPLs, which is not previously reported. Moreover, this interesting result is further confirmed by EDS line scans (Figs. 2 C and D ). In the low-doped NPLs, there is almost no variation in the Mn intensity across the spectrum, as shown in Fig. 2 C. However, in the highly doped NPLs, it increases dramatically at the edges (Fig. 2 D). Notably, the Pb intensity decreases as the Mn intensity increases, indicating that Mn replaces Pb in the octahedral sites coordinated with six Br ions. The observed phase separation from L 2 Pb 1 − x Mn x Br 4 to L 2 MnBr 4 at the edges of the NPLs could be associated with a spinodal decomposition process, wherein the components of a solid solution spontaneously demix from a single thermodynamic phase into two coexisting phases. 51 Additionally, excessive substitutional doping of Mn 2+ at Pb 2+ sites can also induce considerable lattice strain in the NPL structure. To alleviate this strain, the system undergoes structural reorganization, resulting in the transition of most Mn atoms toward the edges of the NPLs. Similar results are seen for (BA) 2 Pb 1−x Mn x Br 4 NPLs, including size and shape morphology, uniform Mn distribution at low doping levels, and phase separation at the edges for higher doping concentrations (Fig. 3 A-D). It is interesting to note that Mn 2+ also substitutionally replaces Pb 2+ sites in BA-based perovskites, similar to the PEA-based counterpart (Fig. 3 D). Thus, the second possibility, that is, different doping sites (substitutional versus interstitial) of Mn in the NPLs with different spacers, can also be excluded, as no significant differences in structural morphology are observed when the spacer ligand is changed from PEA to BA. Local detection of the luminescence in Mn-doped 2D RP perovskite NPLs using cathodoluminescence spectroscopy In order to verify the EDS results and gain deeper insight into the Mn emission, including the exact sites (interior versus edge) of Mn emission within individual NPLs, we measured the local CL using a high-resolution scanning electron microscope (SEM) equipped with a spectral and polarized angle-resolved CL (SPARC) detector. The CL is based on measuring the emitted photons upon interaction with a high-energy electron beam (Fig. 4 A). 52 , 53 The advantage of the CL is its ability to detect local optical properties at the nm scale. In this measurement, we focused the electron beam on a single NPL and collected the CL signal while scanning across the NPLs. The primary difference between CL and PL lies in the excited sample volume, which is significantly smaller in CL compared to PL. Additionally, CL uses a high-energy electron beam, which can excite higher vibrational modes, resulting in a slightly broader CL peak compared to the PL peak. Figures 4 B and C represent 2D CL color maps of highly doped (PEA) 2 Pb 1−x Mn x Br 4 ( x = 0.60) NPLs, with scans performed from the center-to-edge (Fig. 4 B) and edge-to-edge (Fig. 4 C), respectively. The maps reveal two distinct CL emission lines: one corresponding to the band edge at 410 nm and another associated with Mn 2+ states centered at 610 nm, which aligns with the PL data. Notably, the Mn 2+ -related CL is less intense at the center of the NPL, and it gradually increases as the scan progresses toward the edges, with no significant changes in the band-edge CL (Fig. 4 B). When the scanning is limited to the edges, no noticeable variations occur in either the band-edge or Mn 2+ -related CL (Fig. 4 C). For clear visualization, the CL spectra corresponding to the 2D CL map (center to edge) are plotted in Fig. 4 D. The spectra confirm that the Mn 2+ -related CL intensity gradually increases as the scan proceeds from the center to the edge. Moreover, to identify the regions of the NPL contributing most to the CL signal, we performed CL mapping of the entire individual NPL (Fig. 4 E). The results indicate that the majority of the CL signal originates from the edges of the NPLs, which can be attributed to the preferential distribution of Mn ions at these edge sites. Next, we carried out similar measurements on BA-based NPLs, i.e., (BA) 2 Pb 1−x Mn x Br 4 ( x = 0.60). A similar trend is seen, with the only difference being the lower CL intensity from Mn 2+ states compared to the PEA-based NPLs, which is consistent with the PL results (Fig. 4 F-I). CL measurements are also performed for lightly doped (PEA) 2 Pb 1−x Mn x Br 4 ( x = 0.37) NPLs ( Figure S5 ). In this case, almost no changes in the Mn-related CL intensity are detected during the center-to-edge scan ( Figure S5A, B ). Furthermore, CL mapping reveals a uniform distribution of the CL signal across the entire NPL ( Figure S5C ). This result aligns well with the EDS mapping, which also shows a uniform distribution of Mn at lower doping levels. Therefore, CL analysis of highly doped L 2 Pb 1 − x Mn x Br 4 (L = PEA or BA) NPLs reveals that Mn 2+ -related CL increases towards the edges of the NPLs, as the majority of the CL signal originates from these regions. In contrast, for lower doping levels, the absence of changes in the CL signal suggests a uniform distribution of Mn throughout the entire NPL. These results provide valuable insight into the localized optical properties of the material, confirming the exact distribution of Mn emission within the NPLs. We also performed CL measurements on the undoped NPLs ( Figures S6 and S7 ). When scanning was performed from center to edge, the band-edge emission at 410 nm gradually increased in both cases (PEA- and BA-based NPLs) with no spectral shift. The gradual increase in CL intensity can be attributed to the diffusion of excitons toward the NPL edges, which are less passivated by spacer ligands compared to the 2D surface. 17 Synthesis and basic characterization of 2D RP perovskite crystals In order to correlate the observed optical properties with the exact crystal structure obtained from reported single-crystal XRD data, we also synthesized micron-sized bulk crystals of Mn-doped 2D RP perovskites, i.e., L 2 Pb 1 − x Mn x Br 4 (where L = PEA or BA, x = 0, 0.50, 0.70, and 0.90) using the acid-precipitation method. These crystals are synthesized to study the optical and structural differences between NPLs and bulk crystals. Figures S8-10 present photographs of the as-synthesized crystals (under normal light and UV), along with their absorption and PL spectra, and XRD patterns for x varying from 0 to 0.90 for PEA- and BA-based crystals, respectively. Interestingly, similar features in optical properties are observed here as in the case of NPLs, including higher Mn 2+ emission intensity for PEA compared to BA, as well as identical layered structures. It is clear from the UV-illuminated crystals and PL spectra that the PEA-based 2D perovskite crystals exhibit significantly stronger emission than the BA-based counterparts at the same Mn doping level ( Figures S8A and C, and 9A and C ). Furthermore, a significant difference is observed in the actual Mn doping percentage, which is significantly lower in crystals compared to NPLs at the same Mn mole fraction, as determined by ICP-MS ( Tables S4 and S5 ). For example, at x = 0.50, the actual Mn doping percentages in NPLs are 18.23% (PEA) and 18.60% (BA), whereas in crystals, they are considerably lower, at just 0.07% (PEA) and 0.03% (BA). The doping level might be much lower in crystals due to their small surface-to-volume ratio (bulk size), high lattice strain, and lower Mn solubility. Another difference in crystals is the observation of two band-edge emissions at 408 nm and 430 nm, which originate from interior excitons and edge excitons, respectively, as previously reported for bulk crystals. 54 Crystal lattice rigidity and exciton–phonon coupling To decipher the reason behind the higher Mn emission in PEA-based 2D perovskites compared to the BA ones, we examine the structural differences between them more closely. Given the correlation between the material’s structure and exciton–phonon coupling, we specifically analyze the role of crystal rigidity. Figure 5 A presents a comparison of the mean square atomic displacement of various chemical elements in (PEA) 2 PbBr 4 and (BA) 2 PbBr 4 perovskites, derived from their single-crystal XRD structures. 42 Notably, the analysis reveals that BA-based 2D perovskites exhibit a larger root mean squared displacement compared to their counterparts in PEA-based 2D perovskites. This larger atomic displacement suggests that the higher occupation of the existing phonon modes in BA relative to PEA. To gain deeper insight into the electronic structure of these perovskites, we employed density functional theory (DFT) to calculate, firstly, the reduced effective masses of electrons and holes ( Figure S11 ). The in-plane effective masses are slightly larger for PEA ( 𝜇 PEA ∥ = 0.05 m 0 ) than for BA (𝜇 BA ∥ = 0.04 m 0 ), suggesting weaker electron–phonon coupling and thus higher mobility for BA. In contrast, experimental results show higher mobility in PEA-based perovskites, which indicates a significant difference in the phonon structure between the two compounds. 42 , 46 This is confirmed by the computed variation of the energy under isotropic strain (Fig. 5 B), leading to the extraction of the bulk modulus ( B 0 ). We found that a considerably larger value of B 0 for (PEA) 2 PbBr 4 ( B 0, PEA = 14.57 GPa) than for (BA) 2 PbBr 4 ( B 0, BA = 10.90 GPa), revealing that PEA-based perovskites are stiffer than their BA-based counterparts. Next, the PL peaks in these materials typically exhibit an asymmetric shape, characterized by a more pronounced low-energy tail. The extent of this PL tailing can be quantified using the asymmetry factor (AF), defined as the ratio of the integrated PL intensity on the low-energy side to that on the high-energy side, i.e., AF = I LE /I HE . 55 The AF factor is calculated to be 1.63 and 1.82 for (PEA) 2 PbBr 4 and (BA) 2 PbBr 4 , respectively (Fig. 5 C). In general, a higher AF value indicates stronger exciton–phonon coupling and reduced emission from the self-trapped exciton. To quantify the exact exciton–phonon coupling strength, we study low-temperature PL of (PEA) 2 PbBr 4 and (BA) 2 PbBr 4 perovskite crystals, as shown in Fig. 5 D and E , respectively. Generally, at lower temperatures, the exciton–phonon interaction is negligible, and the PL peak width is associated with the lattice disorder. Furthermore, with increasing temperature, phonon scattering becomes more prominent, broadening the PL. The equation correlating PL line width (FWHM) and phonon scattering is given by Eq. 1 , based on Bose-Einstein statistics. 56 Г ( T ) = \(\:\text{Г}\:\left(0\right)+\:\frac{{\text{Г}}_{LO}}{\:\text{e}\text{x}\text{p}\left(\frac{{E}_{LO}}{{\text{K}}_{\text{B}}T}\right)-1}\) (1) In the above equation, Г (0) denotes inhomogeneous broadening at 0 K, Г LO represents exciton–phonon (LO) coupling strength, E LO is the average phonon energy, and K B is the Boltzmann constant. The plot of FWHM versus 1/T is fitted with Eq. 1 (Fig. 5 F), and fitting parameters are given in Table 1 . Among the samples, (PEA) 2 PbBr 4 exhibits a Г LO and E LO value of 1.1 ± 0.1 meV and 58.2 ± 4.0 meV, respectively, which are significantly lower than the corresponding values of 4.2 ± 0.2 meV and 71.2 ± 5.0 meV observed for (BA) 2 PbBr 4 . Also, the PL peak position of (BA) 2 PbBr 4 is shifted more towards lower energy than (PEA) 2 PbBr 4 . These observations suggest stronger exciton–phonon coupling in (BA) 2 PbBr 4 than in (PEA) 2 PbBr 4 , as expected based on the different structures of the intercalated organic spacers. Table 1 Fitting parameters of exciton–phonon coupling Samples Г (0) (meV) Г LO (meV) E LO (meV) (PEA) 2 PbBr 4 43.6 ± 2.0 1.1 ± 0.1 58.2 ± 4.0 (BA) 2 PbBr 4 50.7 ± 3.0 4.2 ± 0.2 71.2 ± 5.0 Importantly, the overall crystal rigidity of 2D perovskites is influenced not only by the molecular rigidity of the organic spacer layer but also by the structural characteristics of the inorganic layer. To examine the effect of the inorganic layer on the crystal rigidity of these perovskites, we employed low-frequency Raman spectroscopy. The Raman spectra of (PEA) 2 PbBr 4 , Mn-doped (PEA) 2 PbBr 4 , (BA) 2 PbBr 4 , and Mn-doped (BA) 2 PbBr 4 are presented in Fig. 5 G. Especially, the BA-based 2D perovskites exhibit a broad low-frequency peak, whereas the PEA-based 2D perovskites show well-resolved Raman peaks at lower wavenumbers. Low-frequency broad Raman features are indicative of strong lattice anharmonicity and dynamic disorder, while sharp and well-resolved peaks are associated with a more ordered and rigid lattice structure. 55 Considering the combined effects of both the organic spacer and the inorganic framework, BA-based perovskites exhibit stronger exciton–phonon coupling, whereas this coupling is weaker in PEA-based perovskites. Therefore, we can conclude that (PEA) 2 PbBr 4 demonstrates a more rigid structure due to its π–π and S-π intermolecular interactions (aromatic) and superior space‑filling ability, leading to reduced lattice vibrations (low phonon amplitude) and, consequently, weaker electron-phonon coupling (Fig. 5 H). 42 , 47 In contrast, (BA) 2 PbBr 4 is softer because it exhibits only van der Waals intermolecular interaction (aliphatic), leading to increased lattice vibrations (high phonon amplitude) and resulting in stronger exciton–phonon coupling. 12 , 46 , 57 , 58 Thus far, it is clear that the observed differences in Mn 2+ emission and PLQY between PEA- and BA-based perovskites can be primarily attributed to variations in the structural properties of the spacers. These structural differences can modulate the excited-state processes in 2D perovskites, including exciton binding energy, interlayer exciton transport, and the spatial overlap between excitonic states and Mn 2+ dopants. Exciton-transport properties Generally, in single-layered 2D perovskites, excitons are primarily localized in-plane, while the presence of insulating organic layers limits out-of-plane transport. In-plane exciton transport occurs via band-like movement of charge carriers, which is interrupted by scattering events with phonons and material defects arising from differences between the spacer ligand. 59 Exciton transport, which critically influences the optoelectronic properties of 2D perovskites, is therefore a key factor in understanding the differences in Mn 2+ PL between PEA-based and BA-based perovskites. The exciton transport in L 2 PbBr 4 and Mn-doped L 2 PbBr 4 (L = PEA or BA) crystals was investigated using ultrafast pump-probe TRM. To specifically probe the diffusion within the 2D layers, all measurements were carried out on large-area 2D crystals (several hundred microns in size; Figure S12 ) rather than on NPL films. For the measurements, the crystals were mechanically exfoliated onto silicon substrates, and experiments were conducted in a vacuum chamber. A 640 nm pump laser was used for excitation through two-photon absorption, and the sample was probed by a 575 nm laser. Both laser beams were focused through an objective lens, and the reflected probe signal was collected by the same objective, filtered by a bandpass (550–600 nm), and directed onto a charged metal–oxide semiconductor camera at different delay times. Two-photon absorption was chosen for excitation to avoid a UV pump that is incompatible with the objective. Transient reflectance, which is defined as \(\:\frac{\varDelta\:R}{R}=\frac{R\left(t\right)-R\left(0\right)}{R\left(0\right)}\) , was calculated at each camera pixel, where \(\:R\left(0\right)\:\) and \(\:R\left(t\right)\:\) are the reflectance values before and after pump excitation, respectively. The \(\:\frac{\varDelta\:R}{R}\:\) signal provides a time-resolved map of exciton diffusion with high temporal and spatial resolution. More details about the instrument and measurement conditions are provided in section S3.4 and Figure S13 . The diffusion maps of undoped and Mn-doped (0.3%) (PEA) 2 PbBr 4 and (BA) 2 PbBr 4 crystals are shown in Fig. 6 A, B, and 6 D, E, respectively. In both undoped samples, the exciton population exhibits rapid spatial expansion shortly after excitation. However, for the doped samples, in addition to fast diffusion, there is a stagnation in spatial expansion, indicating that excitons rapidly diffuse at Mn 2+ dopant sites. To gain deeper insights into the exciton diffusion dynamics, we further examine the temporal progression of the mean-square displacement (𝑀𝑆𝐷) of the exciton distribution, given by Eq. 2 , 46 𝑀𝑆( t ) = σ( t ) 2 − σ(0) 2 (2) Here, σ is the standard deviation at delay time t and zero delay with respect to the pump pulse, evaluated from fitting the Gaussian distribution of intensity profile ( Figure S13D ). A diffusive-to-sub-diffusive transport scheme was adopted here to account for the two subsequent diffusion regimes: (1) a normal diffusive regime with linear behavior, i.e., 𝑀𝑆(𝑡) = 2𝐷𝑡, and (2) a defect-mediated sub-diffusive regime with sublinear behavior, i.e., 𝑀𝑆𝐷(𝑡) = 2𝐷𝑡 𝛼 , where \(\:\:\alpha\:<1\) . Here, D represents the diffusivity, and α is the diffusion exponent. This expression enables us to extract both parameters ( D and α) directly from the experimental data. Figure 6 C and F present 𝑀𝑆𝐷 plots as a function of time for undoped and Mn-doped PEA-and BA-based perovskite crystals, respectively. The measured 𝑀𝑆𝐷(𝑡) are then fitted with the following Equation 3 , 46 $$\:MSD\left(t\right)=\left\{\begin{array}{c}2Dt+c,\:\:t\le\:{t}_{split}\\\:2D\left[{\left(t-{t}_{split}+{t}_{0}\right)}^{\alpha\:}+{t}_{split}-{t}_{0}^{\alpha\:}\right]+c,\:\:t>{t}_{split}\end{array}\right.$$ 3 \(\:{t}_{split}\) is the separation time point between the diffusive and sub-diffusive regime, \(\:c\) is a small offset constant, and \(\:\:{t}_{0}={\alpha\:}^{1/(1-\alpha\:)}\) . The plots are fitted in the range of 0-150 ps using Eq. 3 , and the fitting results are summarized in Table 2 , along with the D value and other parameters. For better visualization, the extracted diffusivity values are plotted as a function of the spacer ligand in Fig. 6 G. The diffusivity value is found to be 32.9 ± 6.0 cm 2 /s (for (PEA) 2 PbBr 4 ), 33.5 ± 4.1 cm 2 /s (for Mn 2+ : (PEA) 2 PbBr 4 ), 12.5 ± 5.0 cm 2 /s (for (BA) 2 PbBr 4 ), and 14.0 ± 3.1 cm 2 /s (for Mn 2+ : (BA) 2 PbBr 4 ). It is important to note that the extracted diffusivity value is approximately twice as high in PEA-based perovskites compared to BA-based perovskites for both undoped and doped samples. This indicates that exciton diffusion is more efficient when PEA is employed as the spacer ligand, whereas it is significantly lower when BA is used. As explained above, the aromatic benzene ring in PEA stiffens the 2D perovskites; in contrast, the aliphatic structure of BA lacks both of these features, resulting in softer 2D perovskites. Consequently, the increased rigidity in PEA-based perovskites suppresses exciton–phonon coupling, leading to higher exciton diffusivity (Fig. 6 H). On the other hand, perovskites incorporating aliphatic BA exhibit stronger exciton–phonon coupling, which ultimately limits the exciton diffusivity due to further formation of polarons. 46 Additionally, a slight improvement in diffusivity value in doped crystals may be attributed to a reduction in defect-induced trapping and the formation of more delocalized excitons. The measured exciton diffusivity is 10 2 times higher than previously reported for L 2 PbBr 4 (L = PEA or BA) crystals measured by PL microscopy. This discrepancy may arise from differences in measurement techniques. 39 , 46 In general, PL microscopy is sensitive to emissive excitons only, while TRM may also pick up a response from the free carriers. On the other hand, a similar surface carrier diffusivity was recently reported for 2D perovskites measured using a four-dimensional scanning ultrafast electron microscopy (4D-SUEM). 60 Thus, these findings suggest that the structural differences between spacer ligands play a crucial role in determining the Mn-based luminescence. Table 2 Exciton diffusion parameters extracted from TRM data Samples Diffusion fitting range (ps) D (cm 2 /s) \(\:\varvec{\alpha\:}\) c (µm 2 ) t split (ps) (PEA) 2 PbBr 4 0 ~ 150 32.9 0.51 0.0077 7.0 Mn (0.3%): (PEA) 2 PbBr 4 0 ~ 150 33.5 0.54 0.0071 6.1 (BA) 2 PbBr 4 0 ~ 150 12.5 0.66 0.0227 15.4 Mn (0.3%): (BA) 2 PbBr 4 0 ~ 150 14.0 0.65 0.0138 13.8 To summarize the TRM characterization, PEA-based 2D perovskites show enhanced Mn 2+ emission due to higher exciton mobility and reduced exciton–phonon coupling from the rigid aromatic spacer, whereas BA-based 2D perovskites suffer from weaker emission owing to limited exciton mobility and stronger exciton–phonon interactions caused by the flexible aliphatic spacer. Further, before reaching Mn 2+ sites, excitons dissociate into free carriers (since the exciton binding energy of Mn-doped perovskites is lower than that of undoped perovskites), which are subsequently transferred to Mn 2+ sites, resulting in Mn 2+ emission within the band edge of the perovskites. 15 , 49 Consequently, PEA-based perovskites exhibit higher Mn 2+ emission and PLQY compared to their BA-based counterparts. Conclusion In summary, we found that spacer ligands in Mn-doped 2D RP lead bromide hybrid perovskites play a crucial role in governing the excited-state properties, specifically, the exciton diffusion, and Mn-based luminescence. RP perovskites incorporating aromatic PEA as the spacer ligand exhibited a significant enhancement in Mn 2+ emission and PLQY, while Mn 2+ emission was substantially lower when aliphatic BA was used as the spacer at similar Mn doping levels. We confirmed that substitutional doping of Mn 2+ ions at Pb 2+ sites occurs in these 2D perovskites and is unaffected by the choice of spacer ligands, as evidenced by XRD and EDS mapping. Additionally, higher doping with Mn 2+ in these perovskites led to the formation of a new phase, L 2 MnBr 4 (L = PEA or BA), at the edges of the NPLs. The reason for improved Mn 2+ emission and PLQY in PEA-based perovskites results from faster charge carrier diffusion toward Mn 2+ sites due to weaker exciton–phonon coupling, whereas the stronger exciton–phonon coupling in BA-based perovskites leads to slower diffusivity and weaker Mn 2+ -based emission. Thus, this study provides valuable insights into how spacer ligands influence the excited-state processes of Mn-doped 2D RP hybrid perovskites. Beyond improving the understanding of Mn-related emission, this work also presents a general framework for exploring the impact of spacer ligands across various 2D perovskite materials. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7431342","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":509582841,"identity":"afab3261-bb01-423b-aaab-a13af57e9856","order_by":0,"name":"Ido Hadar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBElEQVRIiWNgGAWjYBACNoYEBmYGEGJvYGBIKAByGQ42gGR4+Ahq4TkA1GKApIUNpz0wLRJAxQxgLXDTsAM+9uQDzAU11vLmM18nfnhgwJBncPBwA8OPGgYZXFrYeJ4lMM84lm4453buZgmgw4oNDhxsYOw5htthbBI5Bsw8bIcZZ0jnbgBpSdwA1MLA20BIy7/D9jMkz27+AdPC+JeQFt62w4kzJHi3wW1hxmsL0C+HefvSk2fw5G6zSDCQSJwJ1HJY5pgETi3y7ckHH/N8s7adwX52880fFTaJfTeOP3z4psbGnh+HFhA4gMSWAKIDIBEJPBowAH8DKapHwSgYBaNgBAAA5axWFDUYH10AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-0576-9321","institution":"The Hebrew University of Jerusalem","correspondingAuthor":true,"prefix":"","firstName":"Ido","middleName":"","lastName":"Hadar","suffix":""},{"id":509582842,"identity":"8c77b869-f62b-43c8-bc2d-b7c97ca0c678","order_by":1,"name":"Amar Nath Yadav","email":"","orcid":"https://orcid.org/0000-0003-4500-3304","institution":"The Hebrew University of Jerusalem","correspondingAuthor":false,"prefix":"","firstName":"Amar","middleName":"Nath","lastName":"Yadav","suffix":""},{"id":509582843,"identity":"a89011a0-a580-49e6-a771-48bd6bda6ffa","order_by":2,"name":"Du Chen","email":"","orcid":"https://orcid.org/0000-0002-7604-8786","institution":"Yale Univerisy","correspondingAuthor":false,"prefix":"","firstName":"Du","middleName":"","lastName":"Chen","suffix":""},{"id":509582844,"identity":"ee9c0722-5b82-4160-ad93-ac77fccdbcd8","order_by":3,"name":"Shunran Li","email":"","orcid":"https://orcid.org/0000-0003-0428-295X","institution":"Yale University","correspondingAuthor":false,"prefix":"","firstName":"Shunran","middleName":"","lastName":"Li","suffix":""},{"id":509582845,"identity":"e9784bb1-b961-47e8-9a07-5d8d67041720","order_by":4,"name":"Mikaël Kepenekian","email":"","orcid":"https://orcid.org/0000-0001-5192-5896","institution":"Univ Rennes, ENSCR, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)- UMR 6226","correspondingAuthor":false,"prefix":"","firstName":"Mikaël","middleName":"","lastName":"Kepenekian","suffix":""},{"id":509582846,"identity":"36de5359-1f77-45e5-9082-a101b88022f7","order_by":5,"name":"Peijun Guo","email":"","orcid":"https://orcid.org/0000-0001-5732-7061","institution":"Yale University","correspondingAuthor":false,"prefix":"","firstName":"Peijun","middleName":"","lastName":"Guo","suffix":""}],"badges":[],"createdAt":"2025-08-22 06:30:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7431342/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7431342/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90562461,"identity":"846f4f74-af1f-424b-bc91-44be4044690a","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":9750184,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Schematic representation of Mn-doped 2D perovskites with different spacers PEA (top) and BA (bottom). (B, C) PL spectra of (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPLs, with \u003cem\u003ex \u003c/em\u003evarying from 0 to 0.70. (D, E) XRD patterns of (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPLs, with \u003cem\u003ex \u003c/em\u003evarying from 0 to 1. The right panels of Figures D and E show the shifting of the (002) plane towards a larger angle with increasing \u003cem\u003ex\u003c/em\u003e. The inset images in B and C depict photographs of colloidal samples under UV (365 nm).\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/ad4848580865f00b6b9e789c.png"},{"id":90562465,"identity":"7539c9d3-4a14-4e4d-867c-557d91485337","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":20938638,"visible":true,"origin":"","legend":"\u003cp\u003e(A, B) HAADF-STEM image and EDS mapping of (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at low doping (\u003cem\u003ex\u003c/em\u003e = 0.25) (A) and high doping (\u003cem\u003ex\u003c/em\u003e = 0.60) (B). (C, D) Line scans of (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at low doping (\u003cem\u003ex\u003c/em\u003e = 0.25) (C) and high doping (\u003cem\u003ex\u003c/em\u003e = 0.60) (D).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/bd3da7a1df7c9b201c26b61f.png"},{"id":90562468,"identity":"4dd98d9f-d057-4c1d-821c-773016338409","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":14425128,"visible":true,"origin":"","legend":"\u003cp\u003e(A, B) HAADF-STEM images and EDS mapping of (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at low doping (\u003cem\u003ex\u003c/em\u003e = 0.25) (A) and high doping (\u003cem\u003ex\u003c/em\u003e = 0.60) (B). (C, D) Line scans of (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at low doping (\u003cem\u003ex\u003c/em\u003e = 0.25) (C) and high doping (\u003cem\u003ex\u003c/em\u003e = 0.60) (D).\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/87925327ca412c53cc03f78a.png"},{"id":90562462,"identity":"d1d4123f-7b6f-4f55-a1be-602f01bd6ff6","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":13338579,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(A) \u003c/strong\u003eSchematic illustration of the CL mechanism. (B, C) SEM images (left) and 2D CL color maps (right) (where scanning was performed from center-to-edge (B) and edge-to-edge (C)). (D) CL spectra corresponding to the center-to-edge scan, and (E) SEM image and CL mapping of (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at high doping (\u003cem\u003ex\u003c/em\u003e = 0.60). (F, G) SEM images (left) and 2D CL color maps (right) (where scanning was performed from center-to-edge (F) and edge-to-edge (G)). (H) CL spectra corresponding to the center-to-edge scan, and (I) SEM image and CL mapping of (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1-\u003c/sub\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPL at high doping (\u003cem\u003ex\u003c/em\u003e = 0.60). In Figures \u003cstrong\u003eD\u003c/strong\u003e and \u003cstrong\u003eH\u003c/strong\u003e, the CL spectra are normalized to the band-edge emission of the NPL.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/055e8235d5146f07de10a5de.png"},{"id":90562471,"identity":"c1b16d04-1839-4af8-b8bc-b433059ef312","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":15739360,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Atomic displacement of Pb, Br, N, and C in (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e perovskites derived from single-crystal XRD. (B) Energy \u003cem\u003eversus\u003c/em\u003e strain plot of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e for the evaluation of the Bulk modulus. Here, solid lines represent interpolations. (C) Room-temperature PL spectra of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals used for asymmetric factor (AF) calculations. (D) Low temperature PL of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals. (E) Low temperature PL data of (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals. (F) FWHM of PL peak with variation of inverse temperature (1/\u003cem\u003eT\u003c/em\u003e). (G) Low frequency Raman spectra of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and Mn-doped (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals (bottom) and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and Mn-doped (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals (top). (H) Schematic illustration of exciton-phonon coupling in PEA-and BA-based perovskites.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/9ecfc19c73ac009c708de2f6.png"},{"id":90562486,"identity":"09ce5e9a-3f18-4e87-9e74-89e4249b678d","added_by":"auto","created_at":"2025-09-04 06:28:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":16302971,"visible":true,"origin":"","legend":"\u003cp\u003e(A, B) Diffusion map for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (A) and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (B). (C) Mean-square displacement of exciton population over time for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (light pink circle) and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (light blue square). (D, E) Diffusion map for Mn-doped (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (D) and Mn-doped (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (E). (F) Mean-square displacement of exciton population over time for Mn-doped (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (dark pink circle) and Mn-doped (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (dark blue square). Solid lines represent linear fitting (diffusive transport), while dotted lines indicate nonlinear fitting (sub-diffusive transport). (G) Exciton diffusivity as a function of spacer ligand type. (H) Schematic illustration of exciton diffusion in Mn-doped 2D (L)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e perovskites (L = PEA or BA).\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/d70f4ccc0afc8baa82e214d5.png"},{"id":108807037,"identity":"26dcf512-8c13-4a95-a908-84b3cb3fb370","added_by":"auto","created_at":"2026-05-08 15:29:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":79532058,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/4bdcdc20-6bc2-41bd-a5f7-39192215e275.pdf"},{"id":90562754,"identity":"ed900b82-59a0-467f-a220-5dfe1b6c8dde","added_by":"auto","created_at":"2025-09-04 06:36:49","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":5707354,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupportingInformationFinal.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/151770177300676218ab455f.pdf"},{"id":90562460,"identity":"a369751e-3b25-4ed0-ac73-2bcfb6b69273","added_by":"auto","created_at":"2025-09-04 06:28:49","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":983997,"visible":true,"origin":"","legend":"","description":"","filename":"TOC.docx","url":"https://assets-eu.researchsquare.com/files/rs-7431342/v1/659bae232558aa0517208a5b.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn recent years, Ruddlesden-Popper (RP) series of two-dimensional (2D) layered perovskites have attracted significant attention due to their outstanding optoelectronic properties.\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7 CR8\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e The RP perovskites are solution-processed quantum-well structure which can be formed by substituting the A-site cation in three-dimensional (3D) perovskites, ABX\u003csub\u003e3\u003c/sub\u003e ​(where A\u003csup\u003e+\u003c/sup\u003e = Cs, methylammonium (MA), formamidinium (FA); B\u003csup\u003e2+\u003c/sup\u003e = Pb, Sn; and X\u003csup\u003e\u0026minus;\u003c/sup\u003e = Cl, Br, I), with long-chain organic spacer ligand (L) such as butylammonium (BA), phenethylammonium (PEA), among others.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e These structures are described by the chemical formula of L\u003csub\u003e2\u003c/sub\u003eA\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u0026thinsp;\u0026minus;\u0026thinsp;1\u003c/sub\u003ePb\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003eX\u003csub\u003e3\u003cem\u003en\u003c/em\u003e+1\u003c/sub\u003e, where \u003cem\u003en\u003c/em\u003e denotes the number of inorganic octahedral layers.\u003csup\u003e\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e This series exhibits remarkable structural flexibility, enabling bandgap tunability, narrow absorption and photoluminescence (PL) spectra, high exciton binding energy, long charge-carrier diffusion lengths, and enhanced environmental stability imparted by the intercalated organic spacer ligands.\u003csup\u003e\u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19 CR20\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eThe single-layer 2D RP perovskites (L\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1) generally exhibit low PL quantum yield (PLQY) due to self-absorption processes and a high surface-to-volume ratio.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Doping or alloying with foreign metal ions (Cd\u003csup\u003e2+\u003c/sup\u003e, Zn\u003csup\u003e2+\u003c/sup\u003e, Mn\u003csup\u003e2+\u003c/sup\u003e, Sn\u003csup\u003e2+\u003c/sup\u003e, \u003cem\u003eetc.\u003c/em\u003e), has been explored as a strategy to enhance their PLQY and to tune their optoelectronic properties.\u003csup\u003e\u003cspan additionalcitationids=\"CR24 CR25 CR26 CR27 CR28\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Among these metal ions, Mn\u003csup\u003e2+\u003c/sup\u003e doping has been extensively studied due to its unique dual emissions originating from the band edge (high-energy narrow emission) and Mn\u003csup\u003e2+\u003c/sup\u003e states (broad emission at lower energy).\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan additionalcitationids=\"CR31 CR32 CR33 CR34\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e The absence of self-absorption of dopant emission, along with efficient coupling between charge carriers and dopant ions, enables Mn\u003csup\u003e2+\u003c/sup\u003e based emission to achieve an exceptionally high PLQY of up to 97%.\u003csup\u003e36\u003c/sup\u003e These remarkable properties broaden the potential applications of these materials in solid-state lighting, X-ray scintillators, and luminescent solar concentrators.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eWhile considerable advancements have been made in the synthesis and optimization of the optoelectronic properties of Mn-doped 2D RP perovskites, the fundamental understanding of the Mn\u003csup\u003e2+\u003c/sup\u003e doping mechanism and excited-state processes remains limited. For the doping mechanism, the exact sites of Mn\u003csup\u003e2+\u003c/sup\u003e ions (substitutional \u003cem\u003eversus\u003c/em\u003e interstitial) in the inorganic framework remain a subject of extensive debate. Recently, Kuruppu \u003cem\u003eet al.\u003c/em\u003e reported interstitial doping of Mn\u003csup\u003e2+\u003c/sup\u003e in (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, whereas substitutional doping was observed in (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e perovskites.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e In contrast, Ba \u003cem\u003eet al.\u003c/em\u003e and Gao \u003cem\u003eet al.\u003c/em\u003e suggested that the substitutional nature of Mn\u003csup\u003e2+\u003c/sup\u003e doping is present in both PEA- and BA-based 2D perovskites.\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e ​Moreover, the role of spacer ligands in modulating Mn-based luminescence remains poorly understood. In a recent article, it was found that decreasing the chain length of spacer ligands leads to an increase in the PLQY of Mn-doped 2D RP perovskites.\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e Contrarily, the PLQY of 2D perovskites does not depend systematically on the ligand chain length but instead on the electron-phonon interaction.\u003csup\u003e\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e Therefore, a detailed investigation by varying spacer ligands and Mn-doping levels is crucial to fill these gaps.\u003c/p\u003e\u003cp\u003eIn this study, we synthesize Mn-doped 2D RP perovskites in the form of nanoplatelets (NPLs) and bulk crystals, with the chemical formula of L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e, by varying the Mn molar concentration (\u003cem\u003ex\u003c/em\u003e) and using aromatic or aliphatic amines as spacer ligands. Specifically, we select PEA from the aromatic amine series and BA from the aliphatic amine series of spacer ligands to investigate the correlation between the structural modifications and the optical properties of the Mn-doped 2D perovskites. While the choice of spacer ligand has a minor effect on the structure and emission of undoped 2D perovskites, our findings demonstrate that it plays a crucial role in modulating Mn\u003csup\u003e2+\u003c/sup\u003e-based emission. Strong dopant emission is observed when aromatic PEA is used as the spacer ligand, whereas the dopant emission is significantly lower when aliphatic BA is employed. Surprisingly, structural analysis reveals two doping mechanisms for high and low Mn concentrations. At low Mn doping, the dopants are uniformly distributed across the NPL area. However, for high Mn doping, a complete dopant substitution at the edges of the NPLs is observed, accompanied by the formation of a new phase, L\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eThe formation of the new phase at higher doping is supported by high-resolution energy-dispersive X-ray spectroscopy (EDS) mapping and cathodoluminescence (CL) spectroscopy. These doping mechanisms (Mn\u003csup\u003e2+\u003c/sup\u003e replaces Pb\u003csup\u003e2+\u003c/sup\u003e sites) are observed for both PEA and BA structures in NPLs and bulk crystals. Based on the similarities in crystal structure, band-edge emission, and doping mechanisms, we concluded that the differences in Mn emission and PLQY between PEA- and BA-based 2D perovskites lie in the excited-state dynamics and carrier mobility. Therefore, we investigate the exciton transport properties of these perovskites using pump-probe transient reflection microscopy (TRM).\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e This advanced technique enables the direct extraction of exciton diffusivity values, revealing that PEA-based perovskites exhibit nearly twice the diffusivity of their BA-based counterparts, and as a consequence, much higher charge mobility. We attribute this enhancement in mobility to the more rigid crystal structure imparted by the aromatic spacer PEA, which weakens the exciton\u0026ndash;phonon coupling strength. In contrast, the softer lattice associated with the BA spacer leads to stronger exciton\u0026ndash;phonon coupling and consequently reduced mobility. The highly mobile excitons in PEA-based perovskites readily dissociate into free charge carriers, which are efficiently transferred to Mn\u003csup\u003e2+\u003c/sup\u003e sites, thereby enhancing the Mn\u003csup\u003e2+\u003c/sup\u003e emission. In contrast, charge transport is slower in the case of BA, resulting in weaker Mn\u003csup\u003e2+\u003c/sup\u003e emission. These observations suggest a general approach to studying charge mobility in halide perovskites, specifically its correlation with subtle changes in the crystal structure induced by the organic spacers.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cb\u003eInvestigation of the light-emitting properties and precise location of Mn\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e \u003cb\u003eions in Mn-doped 2D RP perovskites\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe colloidal undoped (L\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e) and Mn-doped 2D RP perovskite (L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e) NPLs with varying Mn concentration \u003cem\u003ex\u003c/em\u003e (where \u0026ldquo;\u003cem\u003ex\u0026rdquo;\u003c/em\u003e is defined as the Mn-mole fraction calculated from the precursor ratio Mn/(Mn\u0026thinsp;+\u0026thinsp;Pb)) are synthesized using the ligand-assisted reprecipitation (LARP) method, as described previously.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e More details about synthesis can be found in the supporting information (\u003cb\u003eSI\u003c/b\u003e, \u003cb\u003esection S1)\u003c/b\u003e. In this study, we utilize two different spacer ligands: an aromatic amine, PEA ((PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e), and a linear aliphatic amine, BA ((BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e), with \u003cem\u003ex\u003c/em\u003e varying from 0 to 1. The selection of these two spacers is based on their structural properties. PEA is an aromatic and rigid spacer with a bulky structure due to its phenyl ring, which promotes strong π\u0026ndash;π interactions between adjacent ligands and results in a more ordered and stiffer 2D perovskite lattice. In contrast, BA is an aliphatic and flexible spacer with a linear alkyl chain, leading to greater lattice flexibility and increased structural disorder based solely on van der Waals interactions.\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e Despite these differences, both spacer ligands yield a series of 2D RP perovskites with similar structures and optical properties.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-E represents a schematic of the structure, PL spectra, and color change under UV (365 nm) for the undoped and Mn-doped 2D RP perovskites (PEA \u003cem\u003eversus\u003c/em\u003e BA). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB and \u003cb\u003eC\u003c/b\u003e show the changes in PL with varying \u003cem\u003ex\u003c/em\u003e normalized by the band-edge emission (410 nm). The subsequent changes in the absorption spectra are depicted in \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e. After doping with Mn, the NPLs exhibit band-edge emission and a broad emission centered at 610 nm, which corresponds to the characteristic optically forbidden \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003eT\u003csub\u003e1\u003c/sub\u003e\u0026ndash;\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003eA\u003csub\u003e1\u003c/sub\u003e transition from the Mn\u003csup\u003e2+\u003c/sup\u003e \u003cem\u003ed\u003c/em\u003e-\u003cem\u003ed\u003c/em\u003e state.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e As \u003cem\u003ex\u003c/em\u003e varies from 0 to 0.70, a monotonic increase in the emission from the Mn\u003csup\u003e2+\u003c/sup\u003e state becomes evident for both PEA- and BA-based samples. In particular, two regimes are clearly observed from the PL spectra: for \u003cem\u003ex\u003c/em\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.5, the emission from Mn\u003csup\u003e2+\u003c/sup\u003e states is weaker than the band-edge emission, whereas for \u003cem\u003ex\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.5, the Mn\u003csup\u003e2+\u003c/sup\u003e emission is significantly enhanced and dominates the band-edge emission for both PEA- and BA-based perovskites. Notably, PEA-based NPLs exhibit higher Mn\u003csup\u003e2+\u003c/sup\u003e emission compared to their BA-based counterparts, which can also be validated by the color changes of colloidal NPLs (dispersed in toluene) under UV illumination (365 nm) (insets of Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB and \u003cb\u003eC\u003c/b\u003e). Both PEA- and BA-based undoped (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0) NPLs show similar violet emission. Further, Mn-doped PEA-based NPLs show a color change from pink to orange as \u003cem\u003ex\u003c/em\u003e varies from 0.25 to 0.50. In contrast, for BA-based doped NPLs, a similar transition is seen when \u003cem\u003ex\u003c/em\u003e ranges from 0.50 to 0.70 (higher than PEA). This can also be supported by the changes in CIE color coordinates, which are plotted based on the PL spectra (\u003cb\u003eFigure S2\u003c/b\u003e).\u003c/p\u003e\u003cp\u003eTo further validate these results, we performed PLQY measurements using the direct integrating sphere method (\u003cb\u003eFigure S3\u003c/b\u003e). The undoped perovskites NPLs exhibit relatively low PLQY values of 8.0% and 6.7% for (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, respectively. Upon Mn doping, the PLQY of both perovskites increases remarkably. Specifically, PEA-based 2D perovskites show significantly higher PLQY values (12.5\u0026ndash;75.0%) than the BA-based ones (8.5\u0026ndash;57.0%) across the same range of Mn mole fractions (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.12\u0026ndash;0.70). Here, most of the contribution to the total PLQY originates from the Mn\u003csup\u003e2+\u003c/sup\u003e emission peak rather than the band-edge. The substantial difference in Mn\u003csup\u003e2+\u003c/sup\u003e emission and PLQY between PEA- and BA-based perovskites could be attributed to three main factors: (1) differences in the actual doping percentage at the same nominal Mn concentration (\u003cem\u003ex\u003c/em\u003e), (2) variation in the spatial incorporation of Mn\u003csup\u003e2+\u003c/sup\u003e ions, such as substitutional \u003cem\u003eversus\u003c/em\u003e interstitial sites within the inorganic lead octahedral, and (3) structural differences imposed by the spacer ligands, leading to distinct excited-state charge carrier dynamics. In the following paragraphs, we will examine each of these three possibilities one by one.\u003c/p\u003e\u003cp\u003eTo determine the exact doping percentage of Mn in the 2D perovskite NPLs, we performed inductively coupled plasma mass spectrometry (ICP-MS), and the results are shown in \u003cb\u003eTable S2-3\u003c/b\u003e. When \u003cem\u003ex\u003c/em\u003e (Mn\u003csub\u003efeed\u003c/sub\u003e) varied from 0.12 to 0.70, the Mn atomic percentage (with respect to Pb) ranged from 2.49\u0026ndash;47.05% for PEA-based NPLs and from 2.12\u0026ndash;46.54% for BA-based NPLs. Here, a nonlinear trend between the Mn\u003csub\u003efeed\u003c/sub\u003e and actual doping level (Mn%) is evident, with the conversion yield for Mn\u003csup\u003e2+\u003c/sup\u003e ions being lower than that of Pb\u003csup\u003e2+\u003c/sup\u003e.\u003csup\u003e15,30\u003c/sup\u003e Interestingly, similar Mn doping percentages in both PEA- and BA-based NPLs suggest that the doping level is independent of the spacer ligands, which give rise to the same series of 2D RP perovskites. These findings strongly indicate that the choice of spacer ligands has a negligible effect on the actual Mn doping concentration.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNext, we measured powder X-ray diffraction (XRD) patterns to monitor the structural changes induced by Mn\u003csup\u003e2+\u003c/sup\u003e doping. The XRD patterns for (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e, (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, 0.25, 0.50, 0.70, and 1), are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD and \u003cb\u003eE\u003c/b\u003e, respectively. After careful observation, we notice an overall shift of the diffraction planes to large angles (smaller distances), in both PEA- and BA-based NPLs (right panel of Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD and \u003cb\u003eE)\u003c/b\u003e. This trend is typically observed in doped semiconductors resulting from substitutional doping.\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e In this case, substitutional doping by Mn\u003csup\u003e2+\u003c/sup\u003e at the Pb\u003csup\u003e2+\u003c/sup\u003e site in the octahedral slab leads to lattice contraction, as the six-coordinate crystal ionic radius of Mn\u003csup\u003e2+\u003c/sup\u003e (0.97 \u0026Aring;) is smaller than that of Pb\u003csup\u003e2+\u003c/sup\u003e (1.33 \u0026Aring;).\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e Additionally, it can be observed that the diffraction planes appear at regular intervals, indicating a layered structure.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e The periodicities (Δθ) along the (00\u003cem\u003el\u003c/em\u003e) planes are found to be 5.35\u0026deg; and 6.50\u0026deg; for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e NPLs, respectively. These correspond to average distances of 1.6 nm (PEA) and 1.3 nm (BA) between adjacent lead octahedral layers, calculated using Bragg\u0026rsquo;s diffraction equation. Considering the similar size of a single lead octahedron (~\u0026thinsp;0.6 nm) in both perovskites, the changes in the average distances between adjacent inorganic layers are attributed to the different sizes of the intercalated spacer ligands. The effective sizes of spacers are estimated to be larger for PEA (1 nm) than for BA (0.7 nm) (\u003cb\u003eFigure S4\u003c/b\u003e).\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e In addition, upon careful observation, a new series of planes also appears at regular intervals at higher doping levels (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.5). When we recorded the XRD patterns of L\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e (L\u0026thinsp;=\u0026thinsp;PEA or BA, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1; shown at the top of Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD and \u003cb\u003eE\u003c/b\u003e), the planes closely matched additional planes observed (highlighted in the figure) in L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.70). This indicates that phase separation occurs between L\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e and L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e when Mn\u003csup\u003e2+\u003c/sup\u003e ions are excessively doped (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.5). Similar types of structures, including (PEA)\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e, (PEA)\u003csub\u003e2\u003c/sub\u003eMnCl\u003csub\u003e4\u003c/sub\u003e, CsMnCl\u003csub\u003e3\u003c/sub\u003e, \u003cem\u003eetc.\u003c/em\u003e, have also been reported previously.\u003csup\u003e\u003cspan additionalcitationids=\"CR50\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eTo find the size and shape morphology as well as the distribution of Mn across the NPLs, we performed EDS mapping using scanning transmission electron microscopy (STEM). Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA and \u003cb\u003eB\u003c/b\u003e depict high-angle annular dark-field (HAADF)-STEM images and EDS mapping results for low (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25) and high (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.60) doping of Mn in (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPLs. The size of the NPLs ranges from 500 to 1000 nm, with a rectangular shape and rounded corners, maintaining their 2D structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The EDS mapping depicts that for the low doping levels the Mn atoms are uniformly distributed across the NPLs (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). In contrast, at higher doping levels, the majority of the Mn atoms are concentrated along the edges of the NPLs, in addition to being distributed within the interior (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). This result is well-consistent with the XRD findings and indicates that the phase separation observed in the XRD patterns occurs at the edges of the NPLs, which is not previously reported. Moreover, this interesting result is further confirmed by EDS line scans (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC and \u003cb\u003eD\u003c/b\u003e). In the low-doped NPLs, there is almost no variation in the Mn intensity across the spectrum, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC. However, in the highly doped NPLs, it increases dramatically at the edges (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD). Notably, the Pb intensity decreases as the Mn intensity increases, indicating that Mn replaces Pb in the octahedral sites coordinated with six Br ions. The observed phase separation from L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e to L\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e at the edges of the NPLs could be associated with a spinodal decomposition process, wherein the components of a solid solution spontaneously demix from a single thermodynamic phase into two coexisting phases.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e Additionally, excessive substitutional doping of Mn\u003csup\u003e2+\u003c/sup\u003e at Pb\u003csup\u003e2+\u003c/sup\u003e sites can also induce considerable lattice strain in the NPL structure. To alleviate this strain, the system undergoes structural reorganization, resulting in the transition of most Mn atoms toward the edges of the NPLs.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSimilar results are seen for (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e NPLs, including size and shape morphology, uniform Mn distribution at low doping levels, and phase separation at the edges for higher doping concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-D). It is interesting to note that Mn\u003csup\u003e2+\u003c/sup\u003e also substitutionally replaces Pb\u003csup\u003e2+\u003c/sup\u003e sites in BA-based perovskites, similar to the PEA-based counterpart (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). Thus, the second possibility, that is, different doping sites (substitutional \u003cem\u003eversus\u003c/em\u003e interstitial) of Mn in the NPLs with different spacers, can also be excluded, as no significant differences in structural morphology are observed when the spacer ligand is changed from PEA to BA.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eLocal detection of the luminescence in Mn-doped 2D RP perovskite NPLs using cathodoluminescence spectroscopy\u003c/h2\u003e\u003cp\u003eIn order to verify the EDS results and gain deeper insight into the Mn emission, including the exact sites (interior \u003cem\u003eversus\u003c/em\u003e edge) of Mn emission within individual NPLs, we measured the local CL using a high-resolution scanning electron microscope (SEM) equipped with a spectral and polarized angle-resolved CL (SPARC) detector. The CL is based on measuring the emitted photons upon interaction with a high-energy electron beam (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e,\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e The advantage of the CL is its ability to detect local optical properties at the nm scale. In this measurement, we focused the electron beam on a single NPL and collected the CL signal while scanning across the NPLs. The primary difference between CL and PL lies in the excited sample volume, which is significantly smaller in CL compared to PL. Additionally, CL uses a high-energy electron beam, which can excite higher vibrational modes, resulting in a slightly broader CL peak compared to the PL peak. Figures\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB and \u003cb\u003eC\u003c/b\u003e represent 2D CL color maps of highly doped (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.60) NPLs, with scans performed from the center-to-edge (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB) and edge-to-edge (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC), respectively. The maps reveal two distinct CL emission lines: one corresponding to the band edge at 410 nm and another associated with Mn\u003csup\u003e2+\u003c/sup\u003e states centered at 610 nm, which aligns with the PL data. Notably, the Mn\u003csup\u003e2+\u003c/sup\u003e-related CL is less intense at the center of the NPL, and it gradually increases as the scan progresses toward the edges, with no significant changes in the band-edge CL (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). When the scanning is limited to the edges, no noticeable variations occur in either the band-edge or Mn\u003csup\u003e2+\u003c/sup\u003e -related CL (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). For clear visualization, the CL spectra corresponding to the 2D CL map (center to edge) are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD. The spectra confirm that the Mn\u003csup\u003e2+\u003c/sup\u003e-related CL intensity gradually increases as the scan proceeds from the center to the edge. Moreover, to identify the regions of the NPL contributing most to the CL signal, we performed CL mapping of the entire individual NPL (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eE). The results indicate that the majority of the CL signal originates from the edges of the NPLs, which can be attributed to the preferential distribution of Mn ions at these edge sites.\u003c/p\u003e\u003cp\u003eNext, we carried out similar measurements on BA-based NPLs, i.e., (BA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.60). A similar trend is seen, with the only difference being the lower CL intensity from Mn\u003csup\u003e2+\u003c/sup\u003e states compared to the PEA-based NPLs, which is consistent with the PL results (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eF-I). CL measurements are also performed for lightly doped (PEA)\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026minus;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.37) NPLs (\u003cb\u003eFigure S5\u003c/b\u003e). In this case, almost no changes in the Mn-related CL intensity are detected during the center-to-edge scan (\u003cb\u003eFigure S5A, B\u003c/b\u003e). Furthermore, CL mapping reveals a uniform distribution of the CL signal across the entire NPL (\u003cb\u003eFigure S5C\u003c/b\u003e). This result aligns well with the EDS mapping, which also shows a uniform distribution of Mn at lower doping levels. Therefore, CL analysis of highly doped L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eMn\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (L\u0026thinsp;=\u0026thinsp;PEA or BA) NPLs reveals that Mn\u003csup\u003e2+\u003c/sup\u003e-related CL increases towards the edges of the NPLs, as the majority of the CL signal originates from these regions. In contrast, for lower doping levels, the absence of changes in the CL signal suggests a uniform distribution of Mn throughout the entire NPL. These results provide valuable insight into the localized optical properties of the material, confirming the exact distribution of Mn emission within the NPLs. We also performed CL measurements on the undoped NPLs (\u003cb\u003eFigures S6 and S7\u003c/b\u003e). When scanning was performed from center to edge, the band-edge emission at 410 nm gradually increased in both cases (PEA- and BA-based NPLs) with no spectral shift. The gradual increase in CL intensity can be attributed to the diffusion of excitons toward the NPL edges, which are less passivated by spacer ligands compared to the 2D surface.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eSynthesis and basic characterization of 2D RP perovskite crystals\u003c/h3\u003e\n\u003cp\u003eIn order to correlate the observed optical properties with the exact crystal structure obtained from reported single-crystal XRD data, we also synthesized micron-sized bulk crystals of Mn-doped 2D RP perovskites, i.e., L\u003csub\u003e2\u003c/sub\u003ePb\u003csub\u003e1\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eMn\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003eBr\u003csub\u003e4\u003c/sub\u003e (where L\u0026thinsp;=\u0026thinsp;PEA or BA, \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0, 0.50, 0.70, and 0.90) using the acid-precipitation method. These crystals are synthesized to study the optical and structural differences between NPLs and bulk crystals. \u003cb\u003eFigures S8-10\u003c/b\u003e present photographs of the as-synthesized crystals (under normal light and UV), along with their absorption and PL spectra, and XRD patterns for \u003cem\u003ex\u003c/em\u003e varying from 0 to 0.90 for PEA- and BA-based crystals, respectively. Interestingly, similar features in optical properties are observed here as in the case of NPLs, including higher Mn\u003csup\u003e2+\u003c/sup\u003e emission intensity for PEA compared to BA, as well as identical layered structures. It is clear from the UV-illuminated crystals and PL spectra that the PEA-based 2D perovskite crystals exhibit significantly stronger emission than the BA-based counterparts at the same Mn doping level (\u003cb\u003eFigures S8A and C, and 9A and C\u003c/b\u003e). Furthermore, a significant difference is observed in the actual Mn doping percentage, which is significantly lower in crystals compared to NPLs at the same Mn mole fraction, as determined by ICP-MS (\u003cb\u003eTables S4\u003c/b\u003e and \u003cb\u003eS5\u003c/b\u003e). For example, at \u003cem\u003ex\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.50, the actual Mn doping percentages in NPLs are 18.23% (PEA) and 18.60% (BA), whereas in crystals, they are considerably lower, at just 0.07% (PEA) and 0.03% (BA). The doping level might be much lower in crystals due to their small surface-to-volume ratio (bulk size), high lattice strain, and lower Mn solubility. Another difference in crystals is the observation of two band-edge emissions at 408 nm and 430 nm, which originate from interior excitons and edge excitons, respectively, as previously reported for bulk crystals.\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\n\u003ch3\u003eCrystal lattice rigidity and exciton–phonon coupling\u003c/h3\u003e\n\u003cp\u003eTo decipher the reason behind the higher Mn emission in PEA-based 2D perovskites compared to the BA ones, we examine the structural differences between them more closely. Given the correlation between the material\u0026rsquo;s structure and exciton\u0026ndash;phonon coupling, we specifically analyze the role of crystal rigidity. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA presents a comparison of the mean square atomic displacement of various chemical elements in (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e perovskites, derived from their single-crystal XRD structures.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e Notably, the analysis reveals that BA-based 2D perovskites exhibit a larger root mean squared displacement compared to their counterparts in PEA-based 2D perovskites. This larger atomic displacement suggests that the higher occupation of the existing phonon modes in BA relative to PEA.\u003c/p\u003e\u003cp\u003eTo gain deeper insight into the electronic structure of these perovskites, we employed density functional theory (DFT) to calculate, firstly, the reduced effective masses of electrons and holes (\u003cb\u003eFigure S11\u003c/b\u003e). The in-plane effective masses are slightly larger for PEA (\u003cem\u003e\u0026#120583;\u003c/em\u003e\u003csub\u003ePEA\u003c/sub\u003e∥ = 0.05 m\u003csub\u003e0\u003c/sub\u003e) than for BA (\u0026#120583;\u003csub\u003eBA\u003c/sub\u003e∥ = 0.04 m\u003csub\u003e0\u003c/sub\u003e), suggesting weaker electron\u0026ndash;phonon coupling and thus higher mobility for BA. In contrast, experimental results show higher mobility in PEA-based perovskites, which indicates a significant difference in the phonon structure between the two compounds.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e This is confirmed by the computed variation of the energy under isotropic strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB), leading to the extraction of the bulk modulus (\u003cem\u003eB\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e). We found that a considerably larger value of \u003cem\u003eB\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003eB\u003c/em\u003e\u003csub\u003e0, PEA\u003c/sub\u003e = 14.57 GPa) than for (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (\u003cem\u003eB\u003c/em\u003e\u003csub\u003e0, BA\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;10.90 GPa), revealing that PEA-based perovskites are stiffer than their BA-based counterparts. Next, the PL peaks in these materials typically exhibit an asymmetric shape, characterized by a more pronounced low-energy tail. The extent of this PL tailing can be quantified using the asymmetry factor (AF), defined as the ratio of the integrated PL intensity on the low-energy side to that on the high-energy side, i.e., AF\u0026thinsp;=\u0026thinsp;I\u003csub\u003eLE\u003c/sub\u003e/I\u003csub\u003eHE\u003c/sub\u003e.\u003csup\u003e55\u003c/sup\u003e The AF factor is calculated to be 1.63 and 1.82 for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC). In general, a higher AF value indicates stronger exciton\u0026ndash;phonon coupling and reduced emission from the self-trapped exciton.\u003c/p\u003e\u003cp\u003eTo quantify the exact exciton\u0026ndash;phonon coupling strength, we study low-temperature PL of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e perovskite crystals, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eD and \u003cb\u003eE\u003c/b\u003e, respectively. Generally, at lower temperatures, the exciton\u0026ndash;phonon interaction is negligible, and the PL peak width is associated with the lattice disorder. Furthermore, with increasing temperature, phonon scattering becomes more prominent, broadening the PL. The equation correlating PL line width (FWHM) and phonon scattering is given by \u003cb\u003eEq.\u0026nbsp;1\u003c/b\u003e, based on Bose-Einstein statistics.\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eГ (\u003cem\u003eT\u003c/em\u003e) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{Г}\\:\\left(0\\right)+\\:\\frac{{\\text{Г}}_{LO}}{\\:\\text{e}\\text{x}\\text{p}\\left(\\frac{{E}_{LO}}{{\\text{K}}_{\\text{B}}T}\\right)-1}\\)\u003c/span\u003e\u003c/span\u003e (1)\u003c/p\u003e\u003cp\u003eIn the above equation, Г (0) denotes inhomogeneous broadening at 0 K, Г\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e represents exciton\u0026ndash;phonon (LO) coupling strength, E\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e is the average phonon energy, and K\u003csub\u003eB\u003c/sub\u003e is the Boltzmann constant. The plot of FWHM \u003cem\u003eversus\u003c/em\u003e 1/T is fitted with \u003cb\u003eEq.\u0026nbsp;1\u003c/b\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eF), and fitting parameters are given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Among the samples, (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e exhibits a Г\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e and E\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e value of 1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 meV and 58.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0 meV, respectively, which are significantly lower than the corresponding values of 4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 meV and 71.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 meV observed for (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. Also, the PL peak position of (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e is shifted more towards lower energy than (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e. These observations suggest stronger exciton\u0026ndash;phonon coupling in (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e than in (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, as expected based on the different structures of the intercalated organic spacers.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eFitting parameters of exciton\u0026ndash;phonon coupling\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eГ (0) (meV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eГ\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e (meV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eE\u003csub\u003e\u003cem\u003eLO\u003c/em\u003e\u003c/sub\u003e (meV)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e(PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e43.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e58.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e(BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e50.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e71.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eImportantly, the overall crystal rigidity of 2D perovskites is influenced not only by the molecular rigidity of the organic spacer layer but also by the structural characteristics of the inorganic layer. To examine the effect of the inorganic layer on the crystal rigidity of these perovskites, we employed low-frequency Raman spectroscopy. The Raman spectra of (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, Mn-doped (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e, and Mn-doped (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eG. Especially, the BA-based 2D perovskites exhibit a broad low-frequency peak, whereas the PEA-based 2D perovskites show well-resolved Raman peaks at lower wavenumbers. Low-frequency broad Raman features are indicative of strong lattice anharmonicity and dynamic disorder, while sharp and well-resolved peaks are associated with a more ordered and rigid lattice structure.\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e Considering the combined effects of both the organic spacer and the inorganic framework, BA-based perovskites exhibit stronger exciton\u0026ndash;phonon coupling, whereas this coupling is weaker in PEA-based perovskites. Therefore, we can conclude that (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e demonstrates a more rigid structure due to its π\u0026ndash;π and S-π intermolecular interactions (aromatic) and superior space‑filling ability, leading to reduced lattice vibrations (low phonon amplitude) and, consequently, weaker electron-phonon coupling (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eH).\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e In contrast, (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e is softer because it exhibits only van der Waals intermolecular interaction (aliphatic), leading to increased lattice vibrations (high phonon amplitude) and resulting in stronger exciton\u0026ndash;phonon coupling.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e,\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e Thus far, it is clear that the observed differences in Mn\u003csup\u003e2+\u003c/sup\u003e emission and PLQY between PEA- and BA-based perovskites can be primarily attributed to variations in the structural properties of the spacers. These structural differences can modulate the excited-state processes in 2D perovskites, including exciton binding energy, interlayer exciton transport, and the spatial overlap between excitonic states and Mn\u003csup\u003e2+\u003c/sup\u003e dopants.\u003c/p\u003e\n\u003ch3\u003eExciton-transport properties\u003c/h3\u003e\n\u003cp\u003eGenerally, in single-layered 2D perovskites, excitons are primarily localized in-plane, while the presence of insulating organic layers limits out-of-plane transport. In-plane exciton transport occurs \u003cem\u003evia\u003c/em\u003e band-like movement of charge carriers, which is interrupted by scattering events with phonons and material defects arising from differences between the spacer ligand.\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e Exciton transport, which critically influences the optoelectronic properties of 2D perovskites, is therefore a key factor in understanding the differences in Mn\u003csup\u003e2+\u003c/sup\u003e PL between PEA-based and BA-based perovskites. The exciton transport in L\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and Mn-doped L\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (L\u0026thinsp;=\u0026thinsp;PEA or BA) crystals was investigated using ultrafast pump-probe TRM. To specifically probe the diffusion within the 2D layers, all measurements were carried out on large-area 2D crystals (several hundred microns in size; \u003cb\u003eFigure S12\u003c/b\u003e) rather than on NPL films. For the measurements, the crystals were mechanically exfoliated onto silicon substrates, and experiments were conducted in a vacuum chamber. A 640 nm pump laser was used for excitation through two-photon absorption, and the sample was probed by a 575 nm laser. Both laser beams were focused through an objective lens, and the reflected probe signal was collected by the same objective, filtered by a bandpass (550\u0026ndash;600 nm), and directed onto a charged metal\u0026ndash;oxide semiconductor camera at different delay times. Two-photon absorption was chosen for excitation to avoid a UV pump that is incompatible with the objective. Transient reflectance, which is defined as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\varDelta\\:R}{R}=\\frac{R\\left(t\\right)-R\\left(0\\right)}{R\\left(0\\right)}\\)\u003c/span\u003e\u003c/span\u003e, was calculated at each camera pixel, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:R\\left(0\\right)\\:\\)\u003c/span\u003e\u003c/span\u003eand \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:R\\left(t\\right)\\:\\)\u003c/span\u003e\u003c/span\u003eare the reflectance values before and after pump excitation, respectively. The \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{\\varDelta\\:R}{R}\\:\\)\u003c/span\u003e\u003c/span\u003esignal provides a time-resolved map of exciton diffusion with high temporal and spatial resolution. More details about the instrument and measurement conditions are provided in section \u003cb\u003eS3.4\u003c/b\u003e and \u003cb\u003eFigure S13\u003c/b\u003e. The diffusion maps of undoped and Mn-doped (0.3%) (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e and (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e crystals are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA, B, and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eD, E, respectively. In both undoped samples, the exciton population exhibits rapid spatial expansion shortly after excitation. However, for the doped samples, in addition to fast diffusion, there is a stagnation in spatial expansion, indicating that excitons rapidly diffuse at Mn\u003csup\u003e2+\u003c/sup\u003e dopant sites.\u003c/p\u003e\u003cp\u003eTo gain deeper insights into the exciton diffusion dynamics, we further examine the temporal progression of the mean-square displacement (\u0026#119872;\u0026#119878;\u0026#119863;) of the exciton distribution, given by \u003cb\u003eEq.\u0026nbsp;2\u003c/b\u003e,\u003csup\u003e46\u003c/sup\u003e\u003c/p\u003e\u003cp\u003e\u0026#119872;\u0026#119878;(\u003cem\u003et\u003c/em\u003e) = σ(\u003cem\u003et\u003c/em\u003e)\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e \u0026minus; σ(0)\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e (2)\u003c/p\u003e\u003cp\u003eHere, σ is the standard deviation at delay time t and zero delay with respect to the pump pulse, evaluated from fitting the Gaussian distribution of intensity profile (\u003cb\u003eFigure S13D\u003c/b\u003e). A diffusive-to-sub-diffusive transport scheme was adopted here to account for the two subsequent diffusion regimes: (1) a normal diffusive regime with linear behavior, i.e., \u0026#119872;\u0026#119878;(\u0026#119905;)\u0026thinsp;=\u0026thinsp;2\u0026#119863;\u0026#119905;, and (2) a defect-mediated sub-diffusive regime with sublinear behavior, i.e., \u0026#119872;\u0026#119878;\u0026#119863;(\u0026#119905;)\u0026thinsp;=\u0026thinsp;2\u0026#119863;\u0026#119905;\u003csup\u003e\u0026#120572;\u003c/sup\u003e, where\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:\\alpha\\:\u0026lt;1\\)\u003c/span\u003e\u003c/span\u003e. Here, \u003cem\u003eD\u003c/em\u003e represents the diffusivity, and α is the diffusion exponent. This expression enables us to extract both parameters (\u003cem\u003eD\u003c/em\u003e and α) directly from the experimental data. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC and \u003cb\u003eF\u003c/b\u003e present \u0026#119872;\u0026#119878;\u0026#119863; plots as a function of time for undoped and Mn-doped PEA-and BA-based perovskite crystals, respectively. The measured \u0026#119872;\u0026#119878;\u0026#119863;(\u0026#119905;) are then fitted with the following \u003cb\u003eEquation 3\u003c/b\u003e,\u003csup\u003e46\u003c/sup\u003e\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:MSD\\left(t\\right)=\\left\\{\\begin{array}{c}2Dt+c,\\:\\:t\\le\\:{t}_{split}\\\\\\:2D\\left[{\\left(t-{t}_{split}+{t}_{0}\\right)}^{\\alpha\\:}+{t}_{split}-{t}_{0}^{\\alpha\\:}\\right]+c,\\:\\:t\u0026gt;{t}_{split}\\end{array}\\right.$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{t}_{split}\\)\u003c/span\u003e\u003c/span\u003e is the separation time point between the diffusive and sub-diffusive regime, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:c\\)\u003c/span\u003e\u003c/span\u003e is a small offset constant, and\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:{t}_{0}={\\alpha\\:}^{1/(1-\\alpha\\:)}\\)\u003c/span\u003e\u003c/span\u003e. The plots are fitted in the range of 0-150 ps using Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e3\u003c/span\u003e, and the fitting results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, along with the D value and other parameters. For better visualization, the extracted diffusivity values are plotted as a function of the spacer ligand in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eG. The diffusivity value is found to be 32.9\u0026thinsp;\u0026plusmn;\u0026thinsp;6.0 cm\u003csup\u003e2\u003c/sup\u003e/s (for (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e), 33.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 cm\u003csup\u003e2\u003c/sup\u003e/s (for Mn\u003csup\u003e2+\u003c/sup\u003e: (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e), 12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 cm\u003csup\u003e2\u003c/sup\u003e/s (for (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e), and 14.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 cm\u003csup\u003e2\u003c/sup\u003e/s (for Mn\u003csup\u003e2+\u003c/sup\u003e: (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e).\u003c/p\u003e\u003cp\u003eIt is important to note that the extracted diffusivity value is approximately twice as high in PEA-based perovskites compared to BA-based perovskites for both undoped and doped samples. This indicates that exciton diffusion is more efficient when PEA is employed as the spacer ligand, whereas it is significantly lower when BA is used. As explained above, the aromatic benzene ring in PEA stiffens the 2D perovskites; in contrast, the aliphatic structure of BA lacks both of these features, resulting in softer 2D perovskites. Consequently, the increased rigidity in PEA-based perovskites suppresses exciton\u0026ndash;phonon coupling, leading to higher exciton diffusivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eH). On the other hand, perovskites incorporating aliphatic BA exhibit stronger exciton\u0026ndash;phonon coupling, which ultimately limits the exciton diffusivity due to further formation of polarons.\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e Additionally, a slight improvement in diffusivity value in doped crystals may be attributed to a reduction in defect-induced trapping and the formation of more delocalized excitons. The measured exciton diffusivity is 10\u003csup\u003e2\u003c/sup\u003e times higher than previously reported for L\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e (L\u0026thinsp;=\u0026thinsp;PEA or BA) crystals measured by PL microscopy. This discrepancy may arise from differences in measurement techniques.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e In general, PL microscopy is sensitive to emissive excitons only, while TRM may also pick up a response from the free carriers. On the other hand, a similar surface carrier diffusivity was recently reported for 2D perovskites measured using a four-dimensional scanning ultrafast electron microscopy (4D-SUEM).\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e Thus, these findings suggest that the structural differences between spacer ligands play a crucial role in determining the Mn-based luminescence.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eExciton diffusion parameters extracted from TRM data\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSamples\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDiffusion fitting range (ps)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eD (cm\u003csup\u003e2\u003c/sup\u003e/s)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\varvec{\\alpha\\:}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ec (\u0026micro;m\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003et\u003csub\u003esplit\u003c/sub\u003e (ps)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e(PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026thinsp;~\u0026thinsp;150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e32.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0077\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e7.0\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMn (0.3%): (PEA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026thinsp;~\u0026thinsp;150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e33.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0071\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e6.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e(BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026thinsp;~\u0026thinsp;150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e12.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0227\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e15.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMn (0.3%): (BA)\u003csub\u003e2\u003c/sub\u003ePbBr\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0\u0026thinsp;~\u0026thinsp;150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e14.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.0138\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo summarize the TRM characterization, PEA-based 2D perovskites show enhanced Mn\u003csup\u003e2+\u003c/sup\u003e emission due to higher exciton mobility and reduced exciton\u0026ndash;phonon coupling from the rigid aromatic spacer, whereas BA-based 2D perovskites suffer from weaker emission owing to limited exciton mobility and stronger exciton\u0026ndash;phonon interactions caused by the flexible aliphatic spacer. Further, before reaching Mn\u003csup\u003e2+\u003c/sup\u003e sites, excitons dissociate into free carriers (since the exciton binding energy of Mn-doped perovskites is lower than that of undoped perovskites), which are subsequently transferred to Mn\u003csup\u003e2+\u003c/sup\u003e sites, resulting in Mn\u003csup\u003e2+\u003c/sup\u003e emission within the band edge of the perovskites.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e Consequently, PEA-based perovskites exhibit higher Mn\u003csup\u003e2+\u003c/sup\u003e emission and PLQY compared to their BA-based counterparts.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we found that spacer ligands in Mn-doped 2D RP lead bromide hybrid perovskites play a crucial role in governing the excited-state properties, specifically, the exciton diffusion, and Mn-based luminescence. RP perovskites incorporating aromatic PEA as the spacer ligand exhibited a significant enhancement in Mn\u003csup\u003e2+\u003c/sup\u003e emission and PLQY, while Mn\u003csup\u003e2+\u003c/sup\u003e emission was substantially lower when aliphatic BA was used as the spacer at similar Mn doping levels. We confirmed that substitutional doping of Mn\u003csup\u003e2+\u003c/sup\u003e ions at Pb\u003csup\u003e2+\u003c/sup\u003e sites occurs in these 2D perovskites and is unaffected by the choice of spacer ligands, as evidenced by XRD and EDS mapping. Additionally, higher doping with Mn\u003csup\u003e2+\u003c/sup\u003e in these perovskites led to the formation of a new phase, L\u003csub\u003e2\u003c/sub\u003eMnBr\u003csub\u003e4\u003c/sub\u003e (L\u0026thinsp;=\u0026thinsp;PEA or BA), at the edges of the NPLs. The reason for improved Mn\u003csup\u003e2+\u003c/sup\u003e emission and PLQY in PEA-based perovskites results from faster charge carrier diffusion toward Mn\u003csup\u003e2+\u003c/sup\u003e sites due to weaker exciton\u0026ndash;phonon coupling, whereas the stronger exciton\u0026ndash;phonon coupling in BA-based perovskites leads to slower diffusivity and weaker Mn\u003csup\u003e2+\u003c/sup\u003e-based emission. Thus, this study provides valuable insights into how spacer ligands influence the excited-state processes of Mn-doped 2D RP hybrid perovskites. Beyond improving the understanding of Mn-related emission, this work also presents a general framework for exploring the impact of spacer ligands across various 2D perovskite materials. The insights gained form a basis for designing new, efficient luminescent materials for optoelectronic applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Israel Science Foundation (Grant No. 2078/23) and by the United States-Israel Binational Science Foundation (Grant 2022066).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eStoumpos, C. C. \u003cem\u003eet al.\u003c/em\u003e Ruddlesden-Popper Hybrid Lead Iodide Perovskite 2D Homologous Semiconductors. \u003cem\u003eChem. Mater.\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 2852\u0026ndash;2867 (2016).\u003c/li\u003e\n\u003cli\u003eCao, D. H., Stoumpos, C. C., Farha, O. K., Hupp, J. 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Herein, we study these processes for manganese (Mn)-doped 2D Ruddlesden-Popper perovskites with aromatic phenethylammonium (PEA) and aliphatic butylammonium (BA) spacer ligands. Mn-doping offers a powerful strategy for tuning and enhancing the optoelectronic properties of halide perovskites. Despite notable advancements, the Mn-based emission dynamics and the spacer\u0026rsquo;s influence on the doping mechanism remain poorly understood. We explore Mn-doped 2D perovskites by varying the organic spacer and Mn molar fraction, examining nanoplatelets, and bulk crystals. We observe a complete substitution of Mn\u003csup\u003e2+\u003c/sup\u003e ions at the crystals\u0026rsquo; edges at high doping levels, and a uniform distribution at lower ones, for both spacers. Yet, the Mn-emission differs significantly based on the spacer. PEA-based perovskites exhibit strong emission with a photoluminescence quantum yield of 75%, dropping to 57% for BA. To uncover this contrast, we probed exciton transport using transient reflection microscopy, revealing nearly twice the exciton diffusivity in PEA compared to BA. We further correlate crystal rigidity and exciton\u0026ndash;phonon coupling with diffusivity. This work offers a general framework for studying spacer effects in 2D perovskites, guiding the design of advanced luminescent materials.\u003c/p\u003e","manuscriptTitle":"Spacer Ligands Govern the Charge Mobility and Luminescence in Mn-doped 2D Ruddlesden-Popper Perovskites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-04 06:28:44","doi":"10.21203/rs.3.rs-7431342/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"769e4dba-cfc4-4747-a83a-a4c88786de3f","owner":[],"postedDate":"September 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":54122244,"name":"Physical sciences/Chemistry/Materials chemistry/Optical materials"},{"id":54122245,"name":"Physical sciences/Materials science/Nanoscale materials/Structural properties"},{"id":54122246,"name":"Physical sciences/Nanoscience and technology/Nanoscale materials/Organic\u0026#x2013;inorganic nanostructures"},{"id":54122247,"name":"Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials"}],"tags":[],"updatedAt":"2026-05-08T09:04:43+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-04 06:28:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7431342","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7431342","identity":"rs-7431342","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}