Transition-Metal Doped Armchair Hexagonal SiC Quantum Dots: Insights into Stability, Electronic Structure, and Optoelectronic Properties from First-Principles Calculations

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Teleb, Mahmoud A.S. Sakr, Ghada M Abdelrazek, Omar H. Abd-Elkader, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7654081/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Dec, 2025 Read the published version in Journal of Fluorescence → Version 1 posted 10 You are reading this latest preprint version Abstract The rational design of stable, earth-abundant quantum dots with tunable electronic and optical properties is crucial for advancing sustainable optoelectronic and photocatalytic technologies. In this work, density functional theory (DFT) is employed to investigate pristine and 3d transition-metal (TM)-doped armchair hexagonal silicon carbide quantum dots (AH-SiC-QDs, Si₅₇C₅₇H₃₀). Structural analysis reveals that pristine AH-SiC-QDs exhibit high stability (5.612 eV), surpassing previously reported SiC- and AlN-based QDs. Upon TM incorporation, stability remains robust, with Ni-doping providing the strongest binding and Sc-doping the weakest. Electronic structure calculations show significant dopant-induced modifications in HOMO–LUMO distributions and bandgaps, where Ti- and Sc-doped systems achieve remarkable bandgap narrowing (1.056 and 0.919 eV), enhancing electronic coupling with the host lattice. Optical absorption studies demonstrate pronounced red-shifts into the visible and near-infrared regions, with Sc- and V-doped systems offering extended light-harvesting potential. Mulliken charge and natural bond orbital (NBO) analyses confirm strong donor–acceptor interactions, orbital rehybridization, and enhanced charge transfer, directly linking dopant chemistry to improved catalytic and optoelectronic behavior. These findings establish TM-doped AH-SiC-QDs as versatile and highly tunable platforms for next-generation photocatalysis and energy conversion applications. SiC Quantum Dots Transition Metal Doping Electronic Properties Mulliken charge NBO Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The use of sunlight for water splitting offers a sustainable alternative to fossil fuels while protecting the environment [ 1 – 3 ]. Various semiconductors, including TiO 2 [ 4 , 5 ] and ZnO [ 6 , 7 ] use ultraviolet light, whereas BiVO 4 [ 7 , 8 ] and CdS [ 9 ] operate under visible light. However, these materials require cocatalysts due to rapid electron-hole recombination. Noble metals such as Pt [ 10 ] and Au [ 11 ] are incorporated to enhance charge separation, improving photocatalytic activity [ 12 ]. Silicon carbide (SiC), a third-generation semiconductor, has a suitable band gap (2.4–3.2 eV), high thermal conductivity, and excellent chemical stability [ 7 , 13 ]. While SiC does not inherently produce hydrogen under visible light, its band structure aligns well with water splitting requirements. Studies have demonstrated that β-SiC nanowires absorb visible light and exhibit high photocatalytic hydrogen evolution [ 14 , 15 ]. Enhancing SiC efficiency remains a challenge, though noble metals such as Au [ 16 ] and Pt [ 10 ], along with SiC-CdLa 2 S 4 [ 17 ], have shown improvements. However, cost and scarcity limit their practicality. Nonprecious metal-based cocatalysts, such as MoS 2 , are being explored for charge separation [ 18 , 19 ]. MoS 2 has active edge sites that enhance photocatalytic hydrogen evolution, as demonstrated in g-C 3 N 4 -based systems [ 20 ]. Graphene oxide (GO) is another promising cocatalyst due to its high electron mobility and surface area [ 7 ]. As a catalyst support, SiC has been used with Pd-Au, [ 12 ] Pt, [ 21 ] and Ir [ 13 ] for hydrogenation reactions, showing cooperative catalysis between metal and support [ 22 ]. SiC quantum dots (QDs) exhibit altered surface chemistry[ 23 ], with hydroxyl-enriched SiC QDs enhancing CO 2 hydrogenation [ 24 , 25 ]. Bulk SiC features a 1:1 Si-to-C stoichiometry, high-temperature stability, and applications in high-power devices [ 7 , 26 – 30 ]. Layered SiC nanostructures maintain strong covalent bonds [ 31 ] and have been investigated for hydrogen storage, [ 32 , 33 ] outperforming carbon nanotubes (CNTs) in adsorption [ 34 , 35 ]. Modifications, including defects, [ 36 ] doping, [ 7 , 37 ] and deformation, [ 38 ] improve adsorption energy. Heterogeneous nanostructures, such as h-BCN, exhibit nanodomains (NDs) that modify electronic and catalytic properties [ 39 ]. NDs act as active sites for the hydrogen evolution reaction,[ 40 , 41 ] suggesting that graphene and silicene NDs in SiC monolayers merit further exploration. In this work, we systematically explore the structural, electronic, and optical properties of pristine and 3d transition-metal (TM)-doped armchair hexagonal silicon carbide quantum dots (AH-SiC-QDs) using density functional theory. By examining stability, electronic distributions, bandgap modulation, and light absorption characteristics, we aim to establish how different TM dopants tune the optoelectronic and catalytic performance of AH-SiC-QDs. Special emphasis is given to charge transfer, Mulliken population, and natural bond orbital (NBO) analyses to reveal the underlying donor–acceptor interactions. Our findings provide critical insights into the design of cost-effective, highly stable, and visible-light–responsive QDs, highlighting their potential as promising candidates for next-generation optoelectronic devices and photocatalytic hydrogen and oxygen evolution reactions. 2. Computational methodology The structural optimization and electronic properties (HOMO-LUMO), Mulliken charge, natural bond orbital (NBO) of the studied structures were investigated using density functional theory (DFT) as implemented in Gaussian 16[ 42 – 46 ]. To ensure accurate electronic predictions, the hybrid B3LYP functional [ 47 ] was chosen due to its reliability in similar materials. The 6-31G basis set was employed, providing a balance between computational efficiency and accuracy [ 48 , 49 ], making it a widely used choice in related studies [ 50 – 54 ]. Additionally, van der Waals interactions between the studied compounds and adsorbed intermediate molecules were accounted for by incorporating Grimme’s dispersion correction (gd3) within the B3LYP functional [ 55 ]. 3. Results and discussions 3.1 Optimized structures Building upon our previous study of AHSiC (21 Si and C atoms) and ZHSiC as pyridine sensors [ 50 ], this work extends the investigation to AH-SiC-QDs (57 Si and C atoms) as catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In addition, we explore the effect of doping with 3d transition metals (3d TMs) to catalytic performance. Figure 1 illustrates the optimized structure of AH-SiC-QDs, where the C1 position is identified as the doping site for 3d transition metals (TM). The molecular formula Si₅₇C₅₇H₃₀ indicates that the system consists of an equal number of silicon and carbon atoms, with hydrogen atoms passivating the edges to ensure structural stability. The armchair hexagonal (AH) configuration provides a symmetric arrangement, and the doping at C1 alters the local electronic and structural properties. The transition metals used for doping include Zn, Cu, Ni, Co, Fe, Mn, Cr, V, Ti, and Sc. Table 1 presents critical quantum parameters before and after 3d-TM doping, including bond lengths, bond angles, and binding energy. In the pristine AH-SiC-QDs, the bond lengths of C1-Si2 and C1-Si5 are equal at 1.816 Å, ensuring uniformity in the structure. Upon doping, these bond lengths increase, with Sc doping showing the highest values (2.326 Å and 2.344 Å), indicating weaker bonding and possible structural distortions. In contrast, Ni doping results in the shortest TM-Si bonds (2.104 Å and 2.056 Å), implying a stronger interaction with the quantum dot framework. The Si2-C1-Si5 bond angle in the undoped system is 119.994°, characteristic of sp² hybridization. Fe doping expands this angle to 128.236°, while Cu doping increases it to 124.597°, which may influence the electronic properties. In contrast, Ni and Co doping reduce the bond angles to 106.392° and 106.536°, respectively, leading to localized structural contraction. The C3-Si2-C1-Si5 dihedral angle remains at 180° for all cases, confirming that planarity is preserved in the structure. Table 1 Some important quantum parameters like bond length (Å), dihedral, bond angles (degrees), and binding energy (BE) for AH-SiC-QDs before and after doping with 3d-TM. Compounds C1/TM-Si2 C1/TM-Si5 Si2-C1/TM-Si5 C3-Si2-C1/TM-Si5 BE (eV) AH-SiC-QDs 1.816 1.816 119.994 180 5.612 AH-SiC-QDs-d-Co 2.078 2.135 106.536 180 5.554 AH-SiC-QDs-d-Cu 2.103 2.111 124.597 180 5.548 AH-SiC-QDs-d-Fe 2.109 2.15 128.236 180 5.547 AH-SiC-QDs-d-Ni 2.104 2.056 106.392 180 5.567 AH-SiC-QDs-d-Sc 2.326 2.344 121.954 180 5.516 AH-SiC-QDs-d-Ti 2.284 2.206 123.785 180 5.535 AH-SiC-QDs-d-V 2.193 2.261 118.409 180 5.542 AH-SiC-QDs-d-Zn 2.155 2.155 120.147 180 5.534 AH-SiC-QDs-d-Cr 2.164 2.166 120.169 180 5.551 AH-SiC-QDs-d-Mn 2.142 2.142 120.089 180 5.549 3.2 Stability study Binding energy (BE) is an important indicator of the stability of the AH-SiC-QDs and its related materials. BE = (N C E C + N H E H + E Si N Si + E x N x - Et)/ N t , where N C , N H , N Si , N x and N t denote the numbers of carbon, hydrogen, silicon, 3d-TM and the total number of atoms, respectively. Similarly, E C , E H , E Si , E x and E t represent the total energies of carbon atoms, hydrogen atoms, silicon atoms, 3d-TM atoms, and the final compound, respectively. The BE provides insight into the stability of the doped systems. The pristine AH-SiC-QDs have a BE of 5.612 eV as shown in Table 1 . TM doping slightly reduces the BE, suggesting stabilization of the system. The lowest BE is observed for Sc doping (5.516 eV), indicating a weaker interaction between the TM and the SiC-QDs framework, which may lead to reduced stability. On the other hand, Ni doping exhibits a relatively higher BE (5.567 eV), suggesting stronger binding and enhanced stability. The variations in BE among the doped systems highlight the role of TM atomic size and electronic interactions in modifying the overall stability of AH-SiC-QDs. These findings suggest that the choice of dopant significantly impacts the structural integrity and potential applications of SiC-based quantum dots in electronic and catalytic systems. The BE of AH-SiC-QDs (5.612 eV) is higher than that of AlN-QDs passivated with hydrogen (4.799 eV), fluorine (4.794 eV), and hydroxyl (5.171 eV), indicating greater stability [ 56 ]. Compared to previously studied SiC quantum dots [ 50 ], AH-SiC-QDs also exhibit a higher BE than AHSiC (5.216 eV), AHSiC-e-CHO (5.295 eV), AHSiC-s-CHO (5.228 eV), AHSiC-e-COOH (5.326 eV), and AHSiC-s-COOH (5.261 eV). Similarly, AH-SiC-QDs surpass ZHSiC (5.425 eV), ZHSiC-e-CHO (5.479 eV), ZHSiC-s-CHO (5.428 eV), ZHSiC-e-COOH (5.504 eV), and ZHSiC-s-COOH (5.449 eV). After TM doping, BE slightly decreases, with Sc-doped AH-SiC-QDs having the lowest value (5.516 eV) and Ni-doped the highest (5.567 eV). Despite this reduction, all doped AH-SiC-QDs maintain a BE higher than AlN-QDs and most previously studied SiC-QDs, confirming their superior stability. This suggests that AH-SiC-QDs and their doped derivatives offer enhanced structural robustness, making them promising candidates for stable optoelectronic and catalytic applications. 3.3 Electronic properties Figures 2 (a-h) and S1 (Supplementary File) (a-c) illustrate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions of AH-SiC-QDs and their doped counterparts, demonstrating the impact of TM incorporation on the electronic properties. The pristine AH-SiC-QD exhibits a relatively delocalized HOMO, while LUMO states are more localized, primarily around specific atomic sites. Upon doping, significant variations in electronic distributions occur, suggesting changes in charge transfer characteristics. For Ni, Cu, Co, Sc, Ti, Mn, and Cr doping (Fig. 2 (b-h)), the HOMO states exhibit increased localization around the dopant sites, while the LUMO states are strongly concentrated near the introduced metal atoms. This behavior suggests that these dopants significantly alter the charge density distribution, which can influence optical absorption and reactivity. Notably, Cu and Sc exhibit the most pronounced redistribution of charge density, indicating stronger electronic coupling with the SiC framework. In Figure S1 (a-c), Zn, V, and Ni doping further demonstrate distinct modifications. Zn-doped AH-SiC-QD shows a partially delocalized HOMO, while its LUMO is concentrated around the dopant, suggesting moderate charge confinement. V doping results in highly localized HOMO and LUMO states, indicating strong electronic perturbation. Ni doping, consistent with Fig. 2S1c, induces substantial charge redistribution, further reinforcing its role in modifying the electronic behavior of AH-SiC-QDs. Overall, the observed trends confirm that transition metal doping significantly alters the electronic structure of AH-SiC-QDs. The variation in charge density distribution suggests tunability in electronic and optical properties, making these materials suitable for applications in optoelectronics and catalysis. Figure 3 presents the energy gap (E g ) of AH-SiC-QDs and their doped structures, revealing the impact of dopant incorporation on the electronic properties. The pristine AH-SiC-QDs exhibit the highest E g (2.703 eV), indicating strong quantum confinement. Upon doping, E g decreases in most cases, reflecting enhanced electronic interactions and potential conductivity improvements. Among the doped systems, Ti and Sc induce the most significant bandgap narrowing (1.056 eV and 0.919 eV, respectively), suggesting their strong electronic coupling with the host material. In contrast, Mn- and Zn-doped structures exhibit relatively higher E g values (2.259 eV and 2.133 eV, respectively), implying retained semiconducting behaviour. The variation in E g highlights the tunability of AH-SiC-QDs' electronic properties through selective doping, which is crucial for tailoring their applications in optoelectronics and catalysis. 3.4 Optical analysis The optical absorption spectra presented in Fig. 4 and the excited-state parameters summarized in Table 3 collectively demonstrate the profound influence of TM doping on the electronic and optoelectronic properties of AH-SiC-QDs. The pristine AH-SiC-QDs exhibit the strongest absorption intensity with a maximum peak (λ max ) centered at 420 nm, corresponding to a transition energy (TE) of 2.947 eV (Table 3 ). Upon doping, noticeable red-shifts and intensity modulations are observed, directly linked to the dopant-induced perturbations in the electronic structure. Specifically, Co-, Fe-, Ni-, and Ti-doped systems retain absorption peaks in the visible region (484–518 nm), with moderate oscillator strengths (0.25–0.45), indicating improved optical activity compared to pristine QDs. In contrast, Sc- and V-doped AH-SiC-QDs exhibit remarkable red-shifts with λ max at 611 and 638 nm, respectively, accompanied by significantly reduced oscillator strengths (f), reflecting weaker but extended visible-light absorption. This suggests that Sc and V doping induce mid-gap states that narrow the effective bandgap and promote low-energy transitions. The Zn-doped system also shows a slight red-shift to 477 nm, maintaining relatively strong optical activity. The transition assignments (HOMO→LUMO + n or HOMO–n→LUMO) in Table 3 confirm that doping modifies both the frontier orbital distribution and transition pathways. Notably, V and Sc dopants introduce higher-order transitions (H→L + 3, H–4→L + 2), consistent with their extended absorption into the visible–near-infrared region. Moreover, the transition coefficient (TC) values highlight enhanced charge-transfer characteristics, particularly for V- and Ti-doped systems, which reach 0.715 and 0.532, respectively, implying their potential for efficient light-harvesting and photoinduced charge separation. Overall, the combined evidence from Fig. 4 and Table 3 establishes that TM doping not only tunes the absorption edge but also modulates oscillator strength, charge transfer, and electronic transitions. These findings underscore the capability of AH-SiC-QDs as a versatile platform for optoelectronic and photocatalytic applications, with V- and Sc-doped derivatives being especially promising for visible-light–driven processes. Table 2 Excited-state properties of pristine and TM–doped AH-SiC-QDs, including the number of excited states (ES), maximum absorption wavelength (λ max ), transition energy (TE), main electronic transition (ET), oscillator strength (f), and transition coefficient (TC). Molecules ES λ max (nm) TE (eV) ET f TC AH-SiC-QDs 21 420 2.947 H-8→L 0.340 0.319 AH-SiC-QDs-d-Co 42 518 2.391 H-2→L 0.250 0.512 AH-SiC-QDs-d-Fe 33 506 2.450 H-5→L + 1 0.450 0.375 AH-SiC-QDs-d-Ni 24 484 2.557 H→L + 2 0.380 0.407 AH-SiC-QDs-d-Sc 35 611 2.029 H-4→L + 2 0.045 0.360 AH-SiC-QDs-d-Ti 38 506 2.450 H→L + 9 0.250 0.532 AH-SiC-QDs-d-V 32 638 1.943 H→L + 3 0.060 0.715 AH-SiC-QDs-d-Zn 20 477 2.598 H-9→L 0.300 0.593 3.5 Mulliken charge distribution analysis The Mulliken charge distributions shown in Fig. 5 (a–i) reveal the extent of electronic redistribution in pristine and TM-doped AH-SiC-QDs. For the pristine system (Fig. 5 a), charge is symmetrically distributed across the Si and C atoms, with no localized perturbation, indicating uniform electronic delocalization. Upon doping, distinct charge localization emerges around the incorporated TM atoms, with the Mulliken charge values quantifying their electronic state after embedding. Co, Cu, Ni, and Zn dopants exhibit negative charges (− 0.340, − 0.545, − 0.449, and − 0.611, respectively), signifying that these atoms gain electrons from the AH-SiC-QD framework. The relatively large negative charges on Cu and Zn indicate strong electron-accepting behaviour, suggesting the formation of localized dopant states and enhanced host–dopant hybridization, which may stabilize charge carriers and improve catalytic activity. Ni and Co also act as electron acceptors, though to a lesser extent, reflecting moderate interaction with the host lattice. In contrast, Fe, Sc, Ti, and V show positive charges (+ 0.339, + 0.223, + 0.138, and + 0.054, respectively), indicating electron donation to the AH-SiC-QD framework. Among them, Fe donates the largest fraction of charge, consistent with strong orbital overlap and efficient charge transfer. Sc, Ti, and V donate smaller amounts, with V exhibiting the weakest positive charge, implying shallow dopant levels and explaining its pronounced influence on visible-light absorption (Fig. 4 ) and reduced transition energy (Table 3 ). Overall, the Mulliken charge analysis confirms that TM doping fundamentally alters the electronic landscape of AH-SiC-QDs. Strong electron acceptors (Cu, Zn, Ni, Co) and electron donors (Fe, Sc, Ti, V) introduce different charge-transfer regimes, which directly correlate with the optical and excited-state properties (Fig. 4 and Table 3 ). These results highlight the critical role of dopant electronic configuration in tuning the optoelectronic and catalytic performance of AH-SiC-QDs. 3.5 Natural bond orbital analysis The NBO results presented in Fig. 6 (a–f) and Table 3 reveal the underlying donor–acceptor interactions and stabilization energies (E²) that dictate the electronic response of pristine and TM-doped AH-SiC-QDs. For the pristine system, the strongest delocalization channel is the π(C42–Si100) → n*(Si99) interaction with an E² of 50.61 kcal/mol, highlighting the strong conjugation and inherent stability of the host lattice. Doping with transition metals induces notable variations in these interactions. Co- and Sc-doped AH-SiC-QDs exhibit reduced stabilization energies of 24.35 and 24.13 kcal/mol, respectively, indicating weaker donor–acceptor coupling and a tendency toward localized charge density around the dopant centers. This localization disrupts the extended conjugation network, which is consistent with their diminished optical intensities. By contrast, Fe-, Ni-, and Ti-doped systems retain stronger delocalization, with stabilization energies of 41.60, 43.01, and 44.18 kcal/mol. These relatively high E² values point to robust orbital hybridization and enhanced charge-transfer interactions between the dopant d-orbitals and the SiC lattice. These observations are quantitatively supported by the NBO analysis summarized in Table 3 . The Si₂ atomic charges demonstrate a clear dopant-dependent trend, with significant reductions compared to the pristine system (1.801 e) upon TM incorporation. For example, Sc (0.850 e), Ti (0.947 e), and V (0.953 e) show the largest reductions, confirming their strong electron donation to the SiC lattice. In contrast, Co (1.080 e), Fe (1.108 e), Ni (1.208 e), and Zn (1.088 e) exhibit comparatively higher Si₂ charges, indicating weaker electron donation but stronger charge redistribution within the valence and Rydberg contributions. Notably, the total electron density increases upon doping, reaching values above 13.0 e in Sc-, Ti-, and V-doped systems, a signature of enhanced electron back-donation and orbital hybridization. Meanwhile, the natural electronic configurations reveal distinct rehybridization effects: the increase in 3p populations and small contributions from 4s/4p orbitals indicate mixing of higher-lying states, particularly evident in Sc-, Ti-, and V-doped AH-SiC-QDs. Such reorganization stabilizes the electronic structure and potentially enhances catalytic performance. Thus, Fig. 6 visually captures the dopant-induced redistribution of electron density, while Table 3 provides the quantitative NBO metrics that explain these modifications in terms of charge transfer, electron population shifts, and orbital rehybridization. Together, they confirm that TM doping profoundly tailors the electronic structure of AH-SiC-QDs, which is central to their stability and tunable optoelectronic/catalytic properties. Table 3 Natural bond orbital (NBO) analysis of pristine and TM-doped AH-SiC-QDs, including Si₂ atomic charges, natural population analysis (core, valence, Rydberg, and total electron density), and natural electronic configurations. The results highlight dopant-induced modifications in electron population and orbital occupation, reflecting the electronic redistribution and hybridization effects that govern the stability and optoelectronic properties of the systems. Compound Charge-Si2 Natural population Natural electronic configuration Core Valence Rydberg Total AH-SiC-QDs 1.801 9.996 2.199 0.004 12.199 [core]3S ( 0.71) 3p ( 1.49) AH-SiC-QDs-d-Co 1.080 9.994 2.908 0.017 12.920 [core]3S ( 1.01) 3p ( 1.90) 4S ( 0.01) 4p ( 0.01) AH-SiC-QDs-d-Fe 1.108 9.994 2.881 0.016 12.892 [core]3S ( 1.02 )3p ( 1.87) 4p ( 0.01) AH-SiC-QDs-d-Ni 1.208 9.993 2.781 0.017 12.792 [core]3S ( 0.98) 3p ( 1.80) 4p ( 0.01) AH-SiC-QDs-d-Sc 0.850 9.995 3.138 0.017 13.150 [core]3S ( 1.03) 3p ( 2.11) 4S ( 0.01) 4p ( 0.01) AH-SiC-QDs-d-Ti 0.947 9.995 3.041 0.017 13.053 [core]3S ( 1.04) 3p ( 2.01) 4S ( 0.01) 4p ( 0.01) AH-SiC-QDs-d-V 0.953 9.995 3.035 0.017 13.047 [core]3S ( 1.02) 3p ( 2.01) 4S ( 0.01) 4p ( 0.01) AH-SiC-QDs-d-Zn 1.088 9.996 2.904 0.012 12.912 [core]3S ( 0.99) 3p ( 1.91) 4p ( 0.01) Conclusion In summary, density functional theory was employed to investigate the structural, electronic, and optical behavior of pristine and 3d transition-metal–doped AH-SiC-QDs. The pristine quantum dots exhibited superior stability compared to previously reported SiC- and AlN-based systems, while transition-metal doping slightly reduced but preserved robust binding strength. Dopant incorporation induced significant bandgap modulation, with Sc- and Ti-doped systems showing remarkable narrowing, enabling improved conductivity and light absorption. Optical analyses revealed pronounced red-shifts and extended absorption into the visible and near-infrared regions, particularly for V- and Sc-doped systems, underscoring their potential for efficient light harvesting. Mulliken charge and NBO analyses confirmed strong dopant-dependent charge transfer, orbital rehybridization, and enhanced donor–acceptor interactions, which collectively improve catalytic activity. These findings highlight TM-doped AH-SiC-QDs as stable, tunable, and earth-abundant nanomaterials with great promise for next-generation optoelectronic devices and photocatalytic energy conversion applications. Declarations Ethical Approval : This article does not contain any studies involving animals performed by any of the authors. Consent to Participate: This article does not contain any studies involving animals performed by any of the authors. Consent to Publish : All authors mentioned in the manuscript have given consent for submission and subsequent publication of the manuscript. Conflict of Interest: The authors have declared no conflict of interest. Funding: This work is supported by the National Natural Science Foundation of China (No. 12274361, No. 12474276). This work is supported also by Ongoing Research Funding Program (ORF-2025-468) King Saud University, Riyadh, Saudi Arabia. Author Contribution Nahed H. Teleb: Investigation, Mahmoud A. S. Sakr: Writing-review and editing, Ghada M Abdelrazek: Software and calculations, Omar H. Abd-Elkader: Software and calculations, Mohamed Abdel Rafea: Revising, Hazem Abdelsalam Visualization, and Investigation, Qinfang Zhang: Visualization and Investigation. Acknowledgment: This work is supported by the National Natural Science Foundation of China (No. 12274361, No. 12474276). This work is supported also by Ongoing Research Funding Program (ORF-2025-468) King Saud University, Riyadh, Saudi Arabia. Data availability All data generated or analyzed during this study are included in this published article. Code availability: Not applicable References M.M. Hasan, S.A. Tolba, N.K. Allam, In situ formation of graphene stabilizes zero-valent copper nanoparticles and significantly enhances the efficiency of photocatalytic water splitting, ACS Sustain. Chem. Eng. 6 (2018) 16876–16885. J.-C. Wang, C.-X. Cui, Q.-Q. Kong, C.-Y. Ren, Z. Li, L. Qu, Y. Zhang, K. 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Supplementary Files SupplementaryFile.docx Cite Share Download PDF Status: Published Journal Publication published 06 Dec, 2025 Read the published version in Journal of Fluorescence → Version 1 posted Editorial decision: Revision requested 19 Oct, 2025 Reviews received at journal 18 Oct, 2025 Reviews received at journal 12 Oct, 2025 Reviewers agreed at journal 09 Oct, 2025 Reviewers agreed at journal 08 Oct, 2025 Reviewers agreed at journal 08 Oct, 2025 Reviewers invited by journal 08 Oct, 2025 Editor assigned by journal 24 Sep, 2025 Submission checks completed at journal 24 Sep, 2025 First submitted to journal 18 Sep, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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10:44:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1028379,"visible":true,"origin":"","legend":"\u003cp\u003e(a–h) HOMO/LUMO distributions of AH-SiC-QD and its doped structures with Ni, Cu, Co, Sc, Ti, Mn, and Cr.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/b0e8cbca32d261b063794f46.png"},{"id":94013900,"identity":"e1b62e9b-746f-4c6f-863d-3ce1caf12125","added_by":"auto","created_at":"2025-10-21 10:44:13","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":145758,"visible":true,"origin":"","legend":"\u003cp\u003eEnergy gap (E₉) plot of AH-SiC-QD and its doped structures.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/e72cb3ac9d0623f1ccb32d20.png"},{"id":94013215,"identity":"7cea119b-09e5-44fa-b9ea-4842d5880093","added_by":"auto","created_at":"2025-10-21 10:36:13","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":170998,"visible":true,"origin":"","legend":"\u003cp\u003eSimulated UV–vis absorption spectra of pristine and TM–doped AH-SiC-QDs, illustrating the effect of dopants (Co, Fe, Ni, Sc, Ti, V, and Zn) on optical response. Doping induces red-shifts in the absorption maxima and modulates peak intensities, reflecting significant tuning of electronic transitions and light-harvesting capability.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/6b3d36e843ee19ec3cd07ed4.png"},{"id":94013221,"identity":"603ebed0-275c-4a55-8e3b-b912d5e0df63","added_by":"auto","created_at":"2025-10-21 10:36:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":874001,"visible":true,"origin":"","legend":"\u003cp\u003eMulliken charge distribution of (a) pristine AH-SiC-QDs and (b–i) TM-doped systems (Co, Cu, Fe, Ni, Sc, Ti, V, and Zn). The color map (red → electron depletion, green → electron accumulation) represents the spatial redistribution of electronic charge upon doping. The numerical values denote the Mulliken charge on the dopant atom after incorporation into the AH-SiC-QDs framework, highlighting the extent of charge transfer between the TM and the host lattice.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/24c13c7756967c65e7c334c0.png"},{"id":94014094,"identity":"b70ff3c7-7c05-467e-8953-08ceb5ff6f75","added_by":"auto","created_at":"2025-10-21 10:52:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":585640,"visible":true,"origin":"","legend":"\u003cp\u003eNatural bond orbital (NBO) second-order perturbation analysis of pristine and TM-doped AH-SiC-QDs: (a) AH-SiC-QDs, (b) Co, (c) Fe, (d) Ni, (e) Sc, and (f) Ti. The plots illustrate the dominant donor–acceptor interactions (π→n*) responsible for electronic delocalization, along with their stabilization energies (in kcal/mol). The results show that TM doping significantly modifies orbital overlap and charge delocalization, thereby tuning the electronic stability and reactivity of AH-SiC-QDs.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/7e0a27de0288cca594d59e9e.png"},{"id":97724537,"identity":"b4e3e6ed-6c65-4fcf-b6bd-bfb1c1febd26","added_by":"auto","created_at":"2025-12-08 16:12:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4125115,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/41c4d80f-4ac5-45c9-93f3-acbcfff55f33.pdf"},{"id":94013218,"identity":"b266e654-5185-4627-b498-9755134eb932","added_by":"auto","created_at":"2025-10-21 10:36:13","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":703907,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFile.docx","url":"https://assets-eu.researchsquare.com/files/rs-7654081/v1/66728208063dfa711ea340e9.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Transition-Metal Doped Armchair Hexagonal SiC Quantum Dots: Insights into Stability, Electronic Structure, and Optoelectronic Properties from First-Principles Calculations","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe use of sunlight for water splitting offers a sustainable alternative to fossil fuels while protecting the environment [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Various semiconductors, including TiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] and ZnO [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] use ultraviolet light, whereas BiVO\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and CdS [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] operate under visible light. However, these materials require cocatalysts due to rapid electron-hole recombination. Noble metals such as Pt [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and Au [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] are incorporated to enhance charge separation, improving photocatalytic activity [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Silicon carbide (SiC), a third-generation semiconductor, has a suitable band gap (2.4\u0026ndash;3.2 eV), high thermal conductivity, and excellent chemical stability [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. While SiC does not inherently produce hydrogen under visible light, its band structure aligns well with water splitting requirements. Studies have demonstrated that β-SiC nanowires absorb visible light and exhibit high photocatalytic hydrogen evolution [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Enhancing SiC efficiency remains a challenge, though noble metals such as Au [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and Pt [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], along with SiC-CdLa\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e4\u003c/sub\u003e [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], have shown improvements. However, cost and scarcity limit their practicality. Nonprecious metal-based cocatalysts, such as MoS\u003csub\u003e2\u003c/sub\u003e, are being explored for charge separation [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. MoS\u003csub\u003e2\u003c/sub\u003e has active edge sites that enhance photocatalytic hydrogen evolution, as demonstrated in g-C\u003csub\u003e3\u003c/sub\u003eN\u003csub\u003e4\u003c/sub\u003e-based systems [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Graphene oxide (GO) is another promising cocatalyst due to its high electron mobility and surface area [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. As a catalyst support, SiC has been used with Pd-Au, [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] Pt, [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] and Ir [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] for hydrogenation reactions, showing cooperative catalysis between metal and support [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSiC quantum dots (QDs) exhibit altered surface chemistry[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], with hydroxyl-enriched SiC QDs enhancing CO\u003csub\u003e2\u003c/sub\u003e hydrogenation [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Bulk SiC features a 1:1 Si-to-C stoichiometry, high-temperature stability, and applications in high-power devices [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan additionalcitationids=\"CR27 CR28 CR29\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Layered SiC nanostructures maintain strong covalent bonds [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] and have been investigated for hydrogen storage, [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] outperforming carbon nanotubes (CNTs) in adsorption [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Modifications, including defects, [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] doping, [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] and deformation, [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] improve adsorption energy. Heterogeneous nanostructures, such as h-BCN, exhibit nanodomains (NDs) that modify electronic and catalytic properties [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. NDs act as active sites for the hydrogen evolution reaction,[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] suggesting that graphene and silicene NDs in SiC monolayers merit further exploration. In this work, we systematically explore the structural, electronic, and optical properties of pristine and 3d transition-metal (TM)-doped armchair hexagonal silicon carbide quantum dots (AH-SiC-QDs) using density functional theory. By examining stability, electronic distributions, bandgap modulation, and light absorption characteristics, we aim to establish how different TM dopants tune the optoelectronic and catalytic performance of AH-SiC-QDs. Special emphasis is given to charge transfer, Mulliken population, and natural bond orbital (NBO) analyses to reveal the underlying donor\u0026ndash;acceptor interactions. Our findings provide critical insights into the design of cost-effective, highly stable, and visible-light\u0026ndash;responsive QDs, highlighting their potential as promising candidates for next-generation optoelectronic devices and photocatalytic hydrogen and oxygen evolution reactions.\u003c/p\u003e"},{"header":"2. Computational methodology","content":"\u003cp\u003eThe structural optimization and electronic properties (HOMO-LUMO), Mulliken charge, natural bond orbital (NBO) of the studied structures were investigated using density functional theory (DFT) as implemented in Gaussian 16[\u003cspan additionalcitationids=\"CR43 CR44 CR45\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. To ensure accurate electronic predictions, the hybrid B3LYP functional [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] was chosen due to its reliability in similar materials. The 6-31G basis set was employed, providing a balance between computational efficiency and accuracy [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e], making it a widely used choice in related studies [\u003cspan additionalcitationids=\"CR51 CR52 CR53\" citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. Additionally, van der Waals interactions between the studied compounds and adsorbed intermediate molecules were accounted for by incorporating Grimme\u0026rsquo;s dispersion correction (gd3) within the B3LYP functional [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e].\u003c/p\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Optimized structures\u003c/h2\u003e\u003cp\u003eBuilding upon our previous study of AHSiC (21 Si and C atoms) and ZHSiC as pyridine sensors [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], this work extends the investigation to AH-SiC-QDs (57 Si and C atoms) as catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In addition, we explore the effect of doping with 3d transition metals (3d TMs) to catalytic performance. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the optimized structure of AH-SiC-QDs, where the C1 position is identified as the doping site for 3d transition metals (TM). The molecular formula Si₅₇C₅₇H₃₀ indicates that the system consists of an equal number of silicon and carbon atoms, with hydrogen atoms passivating the edges to ensure structural stability. The armchair hexagonal (AH) configuration provides a symmetric arrangement, and the doping at C1 alters the local electronic and structural properties. The transition metals used for doping include Zn, Cu, Ni, Co, Fe, Mn, Cr, V, Ti, and Sc.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents critical quantum parameters before and after 3d-TM doping, including bond lengths, bond angles, and binding energy. In the pristine AH-SiC-QDs, the bond lengths of C1-Si2 and C1-Si5 are equal at 1.816 \u0026Aring;, ensuring uniformity in the structure. Upon doping, these bond lengths increase, with Sc doping showing the highest values (2.326 \u0026Aring; and 2.344 \u0026Aring;), indicating weaker bonding and possible structural distortions. In contrast, Ni doping results in the shortest TM-Si bonds (2.104 \u0026Aring; and 2.056 \u0026Aring;), implying a stronger interaction with the quantum dot framework. The Si2-C1-Si5 bond angle in the undoped system is 119.994\u0026deg;, characteristic of sp\u0026sup2; hybridization. Fe doping expands this angle to 128.236\u0026deg;, while Cu doping increases it to 124.597\u0026deg;, which may influence the electronic properties. In contrast, Ni and Co doping reduce the bond angles to 106.392\u0026deg; and 106.536\u0026deg;, respectively, leading to localized structural contraction. The C3-Si2-C1-Si5 dihedral angle remains at 180\u0026deg; for all cases, confirming that planarity is preserved in the structure.\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\u003eSome important quantum parameters like bond length (\u0026Aring;), dihedral, bond angles (degrees), and binding energy (BE) for AH-SiC-QDs before and after doping with 3d-TM.\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=\"char\" char=\".\" 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\u003eCompounds\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eC1/TM-Si2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eC1/TM-Si5\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSi2-C1/TM-Si5\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eC3-Si2-C1/TM-Si5\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eBE (eV)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.816\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.816\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e119.994\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.612\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Co\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.078\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.135\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e106.536\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.554\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Cu\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.103\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.111\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e124.597\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.548\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Fe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.109\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e128.236\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.547\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ni\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.104\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.056\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e106.392\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.567\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Sc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.326\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.344\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e121.954\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.516\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ti\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.284\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.206\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e123.785\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.535\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-V\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.193\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.261\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e118.409\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.542\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Zn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.155\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.155\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e120.147\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.534\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Cr\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.164\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.166\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e120.169\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.551\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Mn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.142\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.142\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e120.089\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e180\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e5.549\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Stability study\u003c/h2\u003e\u003cp\u003eBinding energy (BE) is an important indicator of the stability of the AH-SiC-QDs and its related materials. BE = (N\u003csub\u003eC\u003c/sub\u003eE\u003csub\u003eC\u003c/sub\u003e + N\u003csub\u003eH\u003c/sub\u003eE\u003csub\u003eH\u003c/sub\u003e + E\u003csub\u003eSi\u003c/sub\u003eN\u003csub\u003eSi\u003c/sub\u003e + E\u003csub\u003ex\u003c/sub\u003eN\u003csub\u003ex\u003c/sub\u003e- Et)/ N\u003csub\u003et\u003c/sub\u003e, where N\u003csub\u003eC\u003c/sub\u003e, N\u003csub\u003eH\u003c/sub\u003e, N\u003csub\u003eSi\u003c/sub\u003e, N\u003csub\u003ex\u003c/sub\u003e and N\u003csub\u003et\u003c/sub\u003e denote the numbers of carbon, hydrogen, silicon, 3d-TM and the total number of atoms, respectively. Similarly, E\u003csub\u003eC\u003c/sub\u003e, E\u003csub\u003eH\u003c/sub\u003e, E\u003csub\u003eSi\u003c/sub\u003e, E\u003csub\u003ex\u003c/sub\u003e and E\u003csub\u003et\u003c/sub\u003e represent the total energies of carbon atoms, hydrogen atoms, silicon atoms, 3d-TM atoms, and the final compound, respectively. The BE provides insight into the stability of the doped systems. The pristine AH-SiC-QDs have a BE of 5.612 eV as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. TM doping slightly reduces the BE, suggesting stabilization of the system. The lowest BE is observed for Sc doping (5.516 eV), indicating a weaker interaction between the TM and the SiC-QDs framework, which may lead to reduced stability. On the other hand, Ni doping exhibits a relatively higher BE (5.567 eV), suggesting stronger binding and enhanced stability. The variations in BE among the doped systems highlight the role of TM atomic size and electronic interactions in modifying the overall stability of AH-SiC-QDs. These findings suggest that the choice of dopant significantly impacts the structural integrity and potential applications of SiC-based quantum dots in electronic and catalytic systems. The BE of AH-SiC-QDs (5.612 eV) is higher than that of AlN-QDs passivated with hydrogen (4.799 eV), fluorine (4.794 eV), and hydroxyl (5.171 eV), indicating greater stability [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Compared to previously studied SiC quantum dots [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], AH-SiC-QDs also exhibit a higher BE than AHSiC (5.216 eV), AHSiC-e-CHO (5.295 eV), AHSiC-s-CHO (5.228 eV), AHSiC-e-COOH (5.326 eV), and AHSiC-s-COOH (5.261 eV). Similarly, AH-SiC-QDs surpass ZHSiC (5.425 eV), ZHSiC-e-CHO (5.479 eV), ZHSiC-s-CHO (5.428 eV), ZHSiC-e-COOH (5.504 eV), and ZHSiC-s-COOH (5.449 eV). After TM doping, BE slightly decreases, with Sc-doped AH-SiC-QDs having the lowest value (5.516 eV) and Ni-doped the highest (5.567 eV). Despite this reduction, all doped AH-SiC-QDs maintain a BE higher than AlN-QDs and most previously studied SiC-QDs, confirming their superior stability. This suggests that AH-SiC-QDs and their doped derivatives offer enhanced structural robustness, making them promising candidates for stable optoelectronic and catalytic applications.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Electronic properties\u003c/h2\u003e\u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a-h) and S1 (Supplementary File) (a-c) illustrate the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributions of AH-SiC-QDs and their doped counterparts, demonstrating the impact of TM incorporation on the electronic properties. The pristine AH-SiC-QD exhibits a relatively delocalized HOMO, while LUMO states are more localized, primarily around specific atomic sites. Upon doping, significant variations in electronic distributions occur, suggesting changes in charge transfer characteristics. For Ni, Cu, Co, Sc, Ti, Mn, and Cr doping (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (b-h)), the HOMO states exhibit increased localization around the dopant sites, while the LUMO states are strongly concentrated near the introduced metal atoms. This behavior suggests that these dopants significantly alter the charge density distribution, which can influence optical absorption and reactivity. Notably, Cu and Sc exhibit the most pronounced redistribution of charge density, indicating stronger electronic coupling with the SiC framework.\u003c/p\u003e\u003cp\u003eIn Figure S1 (a-c), Zn, V, and Ni doping further demonstrate distinct modifications. Zn-doped AH-SiC-QD shows a partially delocalized HOMO, while its LUMO is concentrated around the dopant, suggesting moderate charge confinement. V doping results in highly localized HOMO and LUMO states, indicating strong electronic perturbation. Ni doping, consistent with Fig.\u0026nbsp;2S1c, induces substantial charge redistribution, further reinforcing its role in modifying the electronic behavior of AH-SiC-QDs. Overall, the observed trends confirm that transition metal doping significantly alters the electronic structure of AH-SiC-QDs. The variation in charge density distribution suggests tunability in electronic and optical properties, making these materials suitable for applications in optoelectronics and catalysis.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the energy gap (E\u003csub\u003eg\u003c/sub\u003e) of AH-SiC-QDs and their doped structures, revealing the impact of dopant incorporation on the electronic properties. The pristine AH-SiC-QDs exhibit the highest E\u003csub\u003eg\u003c/sub\u003e (2.703 eV), indicating strong quantum confinement. Upon doping, E\u003csub\u003eg\u003c/sub\u003e decreases in most cases, reflecting enhanced electronic interactions and potential conductivity improvements. Among the doped systems, Ti and Sc induce the most significant bandgap narrowing (1.056 eV and 0.919 eV, respectively), suggesting their strong electronic coupling with the host material. In contrast, Mn- and Zn-doped structures exhibit relatively higher E\u003csub\u003eg\u003c/sub\u003e values (2.259 eV and 2.133 eV, respectively), implying retained semiconducting behaviour. The variation in E\u003csub\u003eg\u003c/sub\u003e highlights the tunability of AH-SiC-QDs' electronic properties through selective doping, which is crucial for tailoring their applications in optoelectronics and catalysis.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Optical analysis\u003c/h2\u003e\u003cp\u003eThe optical absorption spectra presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e and the excited-state parameters summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e collectively demonstrate the profound influence of TM doping on the electronic and optoelectronic properties of AH-SiC-QDs. The pristine AH-SiC-QDs exhibit the strongest absorption intensity with a maximum peak (λ\u003csub\u003emax\u003c/sub\u003e) centered at 420 nm, corresponding to a transition energy (TE) of 2.947 eV (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Upon doping, noticeable red-shifts and intensity modulations are observed, directly linked to the dopant-induced perturbations in the electronic structure. Specifically, Co-, Fe-, Ni-, and Ti-doped systems retain absorption peaks in the visible region (484\u0026ndash;518 nm), with moderate oscillator strengths (0.25\u0026ndash;0.45), indicating improved optical activity compared to pristine QDs. In contrast, Sc- and V-doped AH-SiC-QDs exhibit remarkable red-shifts with λ\u003csub\u003emax\u003c/sub\u003e at 611 and 638 nm, respectively, accompanied by significantly reduced oscillator strengths (f), reflecting weaker but extended visible-light absorption. This suggests that Sc and V doping induce mid-gap states that narrow the effective bandgap and promote low-energy transitions. The Zn-doped system also shows a slight red-shift to 477 nm, maintaining relatively strong optical activity. The transition assignments (HOMO\u0026rarr;LUMO\u0026thinsp;+\u0026thinsp;n or HOMO\u0026ndash;n\u0026rarr;LUMO) in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e confirm that doping modifies both the frontier orbital distribution and transition pathways. Notably, V and Sc dopants introduce higher-order transitions (H\u0026rarr;L\u0026thinsp;+\u0026thinsp;3, H\u0026ndash;4\u0026rarr;L\u0026thinsp;+\u0026thinsp;2), consistent with their extended absorption into the visible\u0026ndash;near-infrared region. Moreover, the transition coefficient (TC) values highlight enhanced charge-transfer characteristics, particularly for V- and Ti-doped systems, which reach 0.715 and 0.532, respectively, implying their potential for efficient light-harvesting and photoinduced charge separation. Overall, the combined evidence from Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e establishes that TM doping not only tunes the absorption edge but also modulates oscillator strength, charge transfer, and electronic transitions. These findings underscore the capability of AH-SiC-QDs as a versatile platform for optoelectronic and photocatalytic applications, with V- and Sc-doped derivatives being especially promising for visible-light\u0026ndash;driven processes.\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\u003eExcited-state properties of pristine and TM\u0026ndash;doped AH-SiC-QDs, including the number of excited states (ES), maximum absorption wavelength (λ\u003csub\u003emax\u003c/sub\u003e), transition energy (TE), main electronic transition (ET), oscillator strength (f), and transition coefficient (TC).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" 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=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMolecules\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eES\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eλ\u003csub\u003emax\u003c/sub\u003e(nm)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTE (eV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eET\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eTC\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e420\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.947\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH-8\u0026rarr;L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.340\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.319\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Co\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e42\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e518\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.391\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH-2\u0026rarr;L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.512\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Fe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e506\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH-5\u0026rarr;L\u0026thinsp;+\u0026thinsp;1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.375\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ni\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e24\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e484\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.557\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH\u0026rarr;L\u0026thinsp;+\u0026thinsp;2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.380\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.407\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Sc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e611\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.029\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH-4\u0026rarr;L\u0026thinsp;+\u0026thinsp;2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.045\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.360\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ti\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e506\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.450\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH\u0026rarr;L\u0026thinsp;+\u0026thinsp;9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.532\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-V\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e638\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.943\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH\u0026rarr;L\u0026thinsp;+\u0026thinsp;3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.060\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.715\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Zn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e477\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.598\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eH-9\u0026rarr;L\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.593\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Mulliken charge distribution analysis\u003c/h2\u003e\u003cp\u003eThe Mulliken charge distributions shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003e (a\u0026ndash;i) reveal the extent of electronic redistribution in pristine and TM-doped AH-SiC-QDs. For the pristine system (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), charge is symmetrically distributed across the Si and C atoms, with no localized perturbation, indicating uniform electronic delocalization. Upon doping, distinct charge localization emerges around the incorporated TM atoms, with the Mulliken charge values quantifying their electronic state after embedding. Co, Cu, Ni, and Zn dopants exhibit negative charges (\u0026minus;\u0026thinsp;0.340, \u0026minus;\u0026thinsp;0.545, \u0026minus;\u0026thinsp;0.449, and \u0026minus;\u0026thinsp;0.611, respectively), signifying that these atoms gain electrons from the AH-SiC-QD framework. The relatively large negative charges on Cu and Zn indicate strong electron-accepting behaviour, suggesting the formation of localized dopant states and enhanced host\u0026ndash;dopant hybridization, which may stabilize charge carriers and improve catalytic activity. Ni and Co also act as electron acceptors, though to a lesser extent, reflecting moderate interaction with the host lattice. In contrast, Fe, Sc, Ti, and V show positive charges (+\u0026thinsp;0.339, +\u0026thinsp;0.223, +\u0026thinsp;0.138, and +\u0026thinsp;0.054, respectively), indicating electron donation to the AH-SiC-QD framework. Among them, Fe donates the largest fraction of charge, consistent with strong orbital overlap and efficient charge transfer. Sc, Ti, and V donate smaller amounts, with V exhibiting the weakest positive charge, implying shallow dopant levels and explaining its pronounced influence on visible-light absorption (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and reduced transition energy (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Overall, the Mulliken charge analysis confirms that TM doping fundamentally alters the electronic landscape of AH-SiC-QDs. Strong electron acceptors (Cu, Zn, Ni, Co) and electron donors (Fe, Sc, Ti, V) introduce different charge-transfer regimes, which directly correlate with the optical and excited-state properties (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These results highlight the critical role of dopant electronic configuration in tuning the optoelectronic and catalytic performance of AH-SiC-QDs.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Natural bond orbital analysis\u003c/h2\u003e\u003cp\u003eThe NBO results presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e (a\u0026ndash;f) and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e reveal the underlying donor\u0026ndash;acceptor interactions and stabilization energies (E\u0026sup2;) that dictate the electronic response of pristine and TM-doped AH-SiC-QDs. For the pristine system, the strongest delocalization channel is the π(C42\u0026ndash;Si100) \u0026rarr; n*(Si99) interaction with an E\u0026sup2; of 50.61 kcal/mol, highlighting the strong conjugation and inherent stability of the host lattice. Doping with transition metals induces notable variations in these interactions. Co- and Sc-doped AH-SiC-QDs exhibit reduced stabilization energies of 24.35 and 24.13 kcal/mol, respectively, indicating weaker donor\u0026ndash;acceptor coupling and a tendency toward localized charge density around the dopant centers. This localization disrupts the extended conjugation network, which is consistent with their diminished optical intensities. By contrast, Fe-, Ni-, and Ti-doped systems retain stronger delocalization, with stabilization energies of 41.60, 43.01, and 44.18 kcal/mol. These relatively high E\u0026sup2; values point to robust orbital hybridization and enhanced charge-transfer interactions between the dopant d-orbitals and the SiC lattice. These observations are quantitatively supported by the NBO analysis summarized in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The Si₂ atomic charges demonstrate a clear dopant-dependent trend, with significant reductions compared to the pristine system (1.801 e) upon TM incorporation. For example, Sc (0.850 e), Ti (0.947 e), and V (0.953 e) show the largest reductions, confirming their strong electron donation to the SiC lattice. In contrast, Co (1.080 e), Fe (1.108 e), Ni (1.208 e), and Zn (1.088 e) exhibit comparatively higher Si₂ charges, indicating weaker electron donation but stronger charge redistribution within the valence and Rydberg contributions. Notably, the total electron density increases upon doping, reaching values above 13.0 e in Sc-, Ti-, and V-doped systems, a signature of enhanced electron back-donation and orbital hybridization. Meanwhile, the natural electronic configurations reveal distinct rehybridization effects: the increase in 3p populations and small contributions from 4s/4p orbitals indicate mixing of higher-lying states, particularly evident in Sc-, Ti-, and V-doped AH-SiC-QDs. Such reorganization stabilizes the electronic structure and potentially enhances catalytic performance. Thus, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e6\u003c/span\u003e visually captures the dopant-induced redistribution of electron density, while Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e provides the quantitative NBO metrics that explain these modifications in terms of charge transfer, electron population shifts, and orbital rehybridization. Together, they confirm that TM doping profoundly tailors the electronic structure of AH-SiC-QDs, which is central to their stability and tunable optoelectronic/catalytic properties.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eNatural bond orbital (NBO) analysis of pristine and TM-doped AH-SiC-QDs, including Si₂ atomic charges, natural population analysis (core, valence, Rydberg, and total electron density), and natural electronic configurations. The results highlight dopant-induced modifications in electron population and orbital occupation, reflecting the electronic redistribution and hybridization effects that govern the stability and optoelectronic properties of the systems.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" 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\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCompound\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCharge-Si2\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e\u003cp\u003eNatural population\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eNatural electronic configuration\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCore\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eValence\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRydberg\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.801\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.996\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.199\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e12.199\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 0.71)\u003c/sup\u003e3p\u003csup\u003e( 1.49)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Co\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.080\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.994\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.908\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e12.920\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 1.01)\u003c/sup\u003e3p\u003csup\u003e( 1.90)\u003c/sup\u003e4S\u003csup\u003e( 0.01)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Fe\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.108\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.994\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.881\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.016\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e12.892\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 1.02\u003c/sup\u003e)3p\u003csup\u003e( 1.87)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ni\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.208\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.993\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.781\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e12.792\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 0.98)\u003c/sup\u003e3p\u003csup\u003e( 1.80)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Sc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.850\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.995\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.138\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.150\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 1.03)\u003c/sup\u003e3p\u003csup\u003e( 2.11)\u003c/sup\u003e4S\u003csup\u003e( 0.01)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Ti\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.947\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.995\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.041\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.053\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 1.04)\u003c/sup\u003e3p\u003csup\u003e( 2.01)\u003c/sup\u003e4S\u003csup\u003e( 0.01)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-V\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.953\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.995\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.035\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e13.047\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 1.02)\u003c/sup\u003e3p\u003csup\u003e( 2.01)\u003c/sup\u003e4S\u003csup\u003e( 0.01)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAH-SiC-QDs-d-Zn\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.088\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e9.996\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.904\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.012\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e12.912\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e[core]3S\u003csup\u003e( 0.99)\u003c/sup\u003e3p\u003csup\u003e( 1.91)\u003c/sup\u003e4p\u003csup\u003e( 0.01)\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, density functional theory was employed to investigate the structural, electronic, and optical behavior of pristine and 3d transition-metal\u0026ndash;doped AH-SiC-QDs. The pristine quantum dots exhibited superior stability compared to previously reported SiC- and AlN-based systems, while transition-metal doping slightly reduced but preserved robust binding strength. Dopant incorporation induced significant bandgap modulation, with Sc- and Ti-doped systems showing remarkable narrowing, enabling improved conductivity and light absorption. Optical analyses revealed pronounced red-shifts and extended absorption into the visible and near-infrared regions, particularly for V- and Sc-doped systems, underscoring their potential for efficient light harvesting. Mulliken charge and NBO analyses confirmed strong dopant-dependent charge transfer, orbital rehybridization, and enhanced donor\u0026ndash;acceptor interactions, which collectively improve catalytic activity. These findings highlight TM-doped AH-SiC-QDs as stable, tunable, and earth-abundant nanomaterials with great promise for next-generation optoelectronic devices and photocatalytic energy conversion applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u003cb\u003eEthical Approval\u003c/b\u003e:\u003c/strong\u003e\u003cp\u003eThis article does not contain any studies involving animals performed by any of the authors.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent to Participate:\u003c/strong\u003e\u003cp\u003eThis article does not contain any studies involving animals performed by any of the authors.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003e\u003cb\u003eConsent to Publish\u003c/b\u003e:\u003c/strong\u003e\u003cp\u003eAll authors mentioned in the manuscript have given consent for submission and subsequent publication of the manuscript.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConflict of Interest:\u003c/strong\u003e\u003cp\u003eThe authors have declared no conflict of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e\u003cp\u003eThis work is supported by the National Natural Science Foundation of China (No. 12274361, No. 12474276). This work is supported also by Ongoing Research Funding Program (ORF-2025-468) King Saud University, Riyadh, Saudi Arabia.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eNahed H. Teleb: Investigation, Mahmoud A. S. Sakr: Writing-review and editing, Ghada M Abdelrazek: Software and calculations, Omar H. Abd-Elkader: Software and calculations, Mohamed Abdel Rafea: Revising, Hazem Abdelsalam Visualization, and Investigation, Qinfang Zhang: Visualization and Investigation.\u003c/p\u003e\u003ch2\u003eAcknowledgment:\u003c/h2\u003e\u003cp\u003eThis work is supported by the National Natural Science Foundation of China (No. 12274361, No. 12474276). This work is supported also by Ongoing Research Funding Program (ORF-2025-468) King Saud University, Riyadh, Saudi Arabia.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e\u003cp\u003eAll data generated or analyzed during this study are included in this published article.\u003c/p\u003e\u003ch2\u003eCode availability:\u003c/h2\u003e\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eM.M. Hasan, S.A. Tolba, N.K. Allam, In situ formation of graphene stabilizes zero-valent copper nanoparticles and significantly enhances the efficiency of photocatalytic water splitting, ACS Sustain. Chem. Eng. 6 (2018) 16876\u0026ndash;16885.\u003c/li\u003e\n\u003cli\u003eJ.-C. Wang, C.-X. Cui, Q.-Q. Kong, C.-Y. Ren, Z. Li, L. Qu, Y. Zhang, K. Jiang, Mn-doped g-C3N4 nanoribbon for efficient visible-light photocatalytic water splitting coupling with methylene blue degradation, ACS Sustain. Chem. 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Rev. 44 (2015) 5148\u0026ndash;5180.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"SiC Quantum Dots, Transition Metal Doping, Electronic Properties, Mulliken charge, NBO","lastPublishedDoi":"10.21203/rs.3.rs-7654081/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7654081/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe rational design of stable, earth-abundant quantum dots with tunable electronic and optical properties is crucial for advancing sustainable optoelectronic and photocatalytic technologies. In this work, density functional theory (DFT) is employed to investigate pristine and 3d transition-metal (TM)-doped armchair hexagonal silicon carbide quantum dots (AH-SiC-QDs, Si₅₇C₅₇H₃₀). Structural analysis reveals that pristine AH-SiC-QDs exhibit high stability (5.612 eV), surpassing previously reported SiC- and AlN-based QDs. Upon TM incorporation, stability remains robust, with Ni-doping providing the strongest binding and Sc-doping the weakest. Electronic structure calculations show significant dopant-induced modifications in HOMO\u0026ndash;LUMO distributions and bandgaps, where Ti- and Sc-doped systems achieve remarkable bandgap narrowing (1.056 and 0.919 eV), enhancing electronic coupling with the host lattice. Optical absorption studies demonstrate pronounced red-shifts into the visible and near-infrared regions, with Sc- and V-doped systems offering extended light-harvesting potential. Mulliken charge and natural bond orbital (NBO) analyses confirm strong donor\u0026ndash;acceptor interactions, orbital rehybridization, and enhanced charge transfer, directly linking dopant chemistry to improved catalytic and optoelectronic behavior. These findings establish TM-doped AH-SiC-QDs as versatile and highly tunable platforms for next-generation photocatalysis and energy conversion applications.\u003c/p\u003e","manuscriptTitle":"Transition-Metal Doped Armchair Hexagonal SiC Quantum Dots: Insights into Stability, Electronic Structure, and Optoelectronic Properties from First-Principles Calculations","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-21 10:36:08","doi":"10.21203/rs.3.rs-7654081/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-19T06:12:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-18T05:55:55+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-12T06:56:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"27423005207453828213263731448014980464","date":"2025-10-09T10:22:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"160785876433946930972988376921461715401","date":"2025-10-08T16:33:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"245867712980826042560719794688339441599","date":"2025-10-08T12:27:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-08T11:07:52+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-24T05:29:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-24T05:27:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Fluorescence","date":"2025-09-19T03:34:46+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-fluorescence","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jofl","sideBox":"Learn more about [Journal of Fluorescence](https://www.springer.com/journal/10895)","snPcode":"10895","submissionUrl":"https://submission.nature.com/new-submission/10895/3","title":"Journal of Fluorescence","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f6133267-67a9-4308-8274-b4e1e1367412","owner":[],"postedDate":"October 21st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-08T16:08:23+00:00","versionOfRecord":{"articleIdentity":"rs-7654081","link":"https://doi.org/10.1007/s10895-025-04642-y","journal":{"identity":"journal-of-fluorescence","isVorOnly":false,"title":"Journal of Fluorescence"},"publishedOn":"2025-12-06 15:58:28","publishedOnDateReadable":"December 6th, 2025"},"versionCreatedAt":"2025-10-21 10:36:08","video":"","vorDoi":"10.1007/s10895-025-04642-y","vorDoiUrl":"https://doi.org/10.1007/s10895-025-04642-y","workflowStages":[]},"version":"v1","identity":"rs-7654081","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7654081","identity":"rs-7654081","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}