CT state carrier storage-triggered TADP in an organic scintillator

CT state carrier storage-triggered TADP in an organic scintillator | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article CT state carrier storage-triggered TADP in an organic scintillator Shuang-Quan Zang, Qiu-Chen Peng, Yubing Si, Qi Yang, Jia-Wang Yuan, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3916923/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Organic scintillators are among the most promising scintillators due to their inherent merits in terms of heavy metal-free constituents, synthesis designability, affordability of raw materials, and low usage costs 1-6 . However, the limited X-ray excited luminescence (XEL) property of organic scintillators affects their application. To date, the main approaches for improving the XEL property of organic scintillators have focused on introducing heavy atoms to increase the absorbance of X-ray and establishing new luminescence pathways, such as thermally activated delayed fluorescence (TADF), to increase the exciton utilization efficiency 7-10 . Even so, the XEL property of organic scintillators is not ideal compared with that of commercial inorganic scintillators. In this work, a highly stable charge transfer (CT) state trap was introduced into the design of an organic scintillator. Combined with a unique thermally activated delayed phosphorescence (TADP) process, highly efficient capture and conversion of high-energy carriers are realized. As a result, the exciton generation efficiency dramatically increases, with an ultrahigh light yield (LY), and X-ray afterglow imaging at room temperature is achieved for the first time. This work provides a brand-new strategy for the design of high-performance organic scintillators. Physical sciences/Chemistry/Materials chemistry/Optical materials Physical sciences/Chemistry/Physical chemistry/Excited states Figures Figure 1 Figure 2 Figure 3 Figure 4 Main text In recent years, X-ray detection technology has received increasing attention in various fields, such as high-energy physics, medical diagnosis, and nondestructive testing 11-15 . As the core material of X-ray detection technology, scintillators directly determine the detection performance and have become the most important optoelectronic material in X-ray detection technology 16-21 . At present, the mainstream research hotspot of scintillators is inorganic semiconductors and inorganic-organic hybrid materials due to their high light yield (LY) and multiple luminescence properties 22-26 . However, harsh preparation conditions and poor stability usually lead to high usage costs for traditional scintillators. Moreover, the heavy metals contained in these scintillators pose a potential environmental pollution risk, greatly limiting their popularity and application. Small-molecule organic materials have many advantages, such as heavy metal-free constituents, synthesis designability, affordable raw materials, and low usage costs 1-6 . These materials have achieved great success in optoelectronic fields, including in organic light-emitting diodes (OLEDs), photovoltaic devices and field-effect transistors, which means that they have broad development potential in the field of scintillators. In fact, the scintillation behaviour of small-molecule organic materials under X-ray irradiation was discovered for anthracene crystals as early as 1947 27 . However, the development of organic scintillators has been very slow over the past several decades. The X-ray excited luminescence (XEL) mechanism of an organic scintillator is shown in Fig. 1a, which can be divided into three stages 28,29 . In the first stage ( Step I ), high-energy X-ray is absorbed by atoms through the photoelectric effect and Compton scattering to produce high-energy electrons. In the second stage ( Step II ), through inelastic electron scattering and the Auger effect, some of the high-energy electrons produce secondary electrons and holes, which interact to produce excitons. In the third stage ( Step III ), visible luminescence is produced by the radiative transition process of the excitons. Because of the lack of heavy atoms, most organic scintillators exhibit weak X-ray absorption, and the spin-forbidden transition from the triplet excited state to the singlet ground state limits their exciton utilization. In recent years, heavy atoms such as bromine and iodine have been added to organic scintillators to increase their X-ray absorption, while fast thermally activated up-conversion processes and aggregation-induced emission (AIE) moieties have been introduced into the design of organic scintillators to increase exciton utilization 7-10 . However, very few of these materials have conspicuous scintillation properties, and the LY of most small-molecule organic materials is far less than that of inorganic materials. The cause of the above results is that in Step II , many high-energy electrons with inappropriate energy cannot effectively produce secondary electrons and holes. To solve this problem, a donor-acceptor (D-A)-doped AIE system of TPP-3C2B:DMA is prepared in this work, which constructs a charge transfer (CT) state trap to capture high-energy electrons. The triplet-triplet energy transfer (TTET) leads to a unique thermally activated delayed phosphorescence (TADP) process, providing a new pathway for significantly enhancing the exciton generation efficiency, resulting in an ultrahigh LY. Moreover, the presence of a CT state trap endows the organic scintillator with ultralong afterglow at room temperature, realizing X-ray afterglow imaging. Synthesis and characterization of scintillation properties TPP-3C2B:DMA was easily prepared by cocrystallization of TPP-3C2B and DMA 30 . The doping ratio of DMA was 0.5%, which could not be determined by single-crystal X-ray diffraction (SCXRD) or powder X-ray diffraction (PXRD) (Figs. 1b-c) but could be confirmed by 1 H-NMR (Supplementary Figs. 5-6). The preparation method of TPP-3C2B:DMA crystals is very mild and simple, and gram-scale preparation of millimetre-scale crystals can be easily achieved under laboratory conditions (Figs. 1d-e). TPP-3C2B:DMA has a strong XEL under X-ray excitation. As shown in Fig. 2a, its XEL intensity not only far exceeds that of the plastic organic scintillator EJ-200 and the classical organic scintillator anthracene but also surpasses that of many commercially available inorganic scintillators, such as Bi 4 Ge 3 O 12 (BGO). Next, using BGO as a standard sample, according to the curves of the X-ray attenuation efficiency with the X-ray energy and sample thickness (Figs. 2b-c) and the XEL spectral integral area ratio of TPP-3C2B:DMA to BGO (Fig. 2d and Supplementary Fig. 7), the relative LY of TPP-3C2B:DMA can be calculated as 76600 photon MeV -1 , which is currently the highest reported LY of organic scintillators. In medical applications, the X-ray dose should be as low as possible to minimize harm to the human body while ensuring completion of detection. As shown in Figs. 2e-f, TPP-3C2B:DMA has an ultrasensitive response to X-ray, and its XEL intensity presents a good linear relationship with the X-ray dose. The lowest detection limit of TPP-3C2B:DMA calculated by the 3s method is 12.3 nGy s -1 , which is far lower than the minimum dose requirement for medical detection (5.5 mGy s -1 ) 31 . In addition, for scintillators, stable cycling performance is also a very important usage indicator. As shown in Fig. 2g, TPP-3C2B:DMA can still well maintain its XEL intensity after being continuously exposed to high-dose X-ray (278 μGy s -1 ) for 60 min or after cycling on and off 60 times. Most importantly, TPP-3C2B:DMA can exhibit a significant 7-hour afterglow observable by the naked eye and a time curve after stopping the 50 kV X-ray excitation (Figs. 2h-i and Supplementary Video 1), which is the first ultralong afterglow observed for a small-molecule organic material under X-ray excitation. Investigation of the scintillation mechanism To understand the influence of the CT state on the LY and afterglow of TPP-3C2B:DMA, undoped TPP-3C2B was selected as a control compound. As shown in Supplementary Figs. 8-10, the LY of TPP-3C2B is much lower than that of TPP-3C2B:DMA, although the photoluminescence intensity of the former is still 40% that of the latter. The X-ray absorbance capacity of TPP-3C2B is almost the same as that of TPP-3C2B:DMA (Supplementary Fig. 11), which means that step I is not the origin of their different XEL properties. Moreover, TPP-3C2B and TPP-3C2B:DMA have almost the same crystal structure (Figs. 1b-c and Supplementary Fig. 12), ensuring their similar nonradiative transition processes induced by molecular packing. That is, the influence of step III on their different XEL properties can also be excluded. Thus, the difference in LY between TPP-3C2B and TPP-3C2B:DMA is mainly attributed to the ability of the CT state to capture electrons and holes. As shown in Supplementary Fig. 13, there are two lifetimes in TPP-3C2B, 0.3 μs and 74 ms, corresponding to thermally activated delayed fluorescence (TADF) and phosphorescence, respectively. For TPP-3C2B:DMA, three lifetimes are observed, 3.3 μs, 310 ms and 7 h, corresponding to TADF, TADP and afterglow, respectively. The origin of the afterglow was investigated by time-dependent emission decay measurements at different temperatures. As shown in Fig. 3a, the afterglow decay curves can be well fit with second-order reaction kinetics (1/ I µ t), suggesting that the generation of excitons is a second-order kinetics process. This result is obtained because the recombination process occurs between electrons and holes and because the concentrations of electrons and holes are equal; thus, the reaction rate should be proportional to the square of the electron concentration (or hole concentration), i.e., a second-order reaction. This result demonstrates that the CT state can effectively capture and store carriers, which is the origin of the intense XEL. Furthermore, the activation energy ( E a ), i.e., the depth of the CT state trap, can be evaluated according to the Arrhenius expression: ln k = - E a /RT + constant (1) where T is the temperature and R is the ideal gas constant. The depth of the CT state trap is calculated to be 35.5 kJ mol -1 (0.37 eV) (Fig. 3b). As shown in Supplementary Fig. 14, the same result can be obtained by fitting the photoluminescence decay curves, demonstrating that the photoexcited afterglow and X-ray excited afterglow have the same source, that is, the TADP from the CT state to the first excited triplet state (T 1 ). The afterglow of TPP-3C2B:DMA and TPP-3C2B with changing temperature was further investigated 32,33 . The samples were irradiated by X-ray at 83 K. When the X-ray was shut off, the emission intensity at 510 nm was recorded, and the temperature was gradually increased from 83 K to room temperature (Fig. 3c). As shown, only a very short afterglow can be observed at 83 K, which originates from the enhanced phosphorescence at low temperatures. When the temperature is increased, intense afterglow emerges and reaches a maximum at 120 K. Interestingly, when the temperature is further increased, the afterglow quickly disappears for TPP-3C2B, while a new afterglow peak emerges for TPP-3C2B:DMA at 150 K that reaches a maximum at 220 K. A proposed mechanism for these phenomena is shown in Fig. 3d and Supplementary Fig. 15. For TPP-3C2B, there is an intramolecular CT (intra-CT) state derived from the charge transfer between the Br - and phosphonium cations 30,34 . Carriers produced by X-ray irradiation are stored in the intra-CT state of TPP-3C2B at 83 K. With an increase in temperature, a TADP process occurs, and visible afterglow emerges. However, because the intra-CT state is unstable at high temperatures, the afterglow quickly disappears when the temperature is further increased. In contrast, there is another intermolecular CT (inter-CT) state in addition to the intra-CT state for TPP-3C2B:DMA, and the depth of the inter-CT state trap is deeper than that of the intra-CT state. As a result, TPP-3C2B:DMA and TPP-3C2B exhibit almost the same afterglow change at 83 K-120 K. When the temperature is further increased, the carriers stored in the inter-CT state are activated, and exciton formation reaches a maximum at 220 K. At room temperature, this TADP process is maintained, resulting in visible afterglow. Under UV light, similar afterglow changes can be observed for TPP-3C2B:DMA and TPP-3C2B (Supplementary Fig. 16). However, the excitons produced by UV light irradiation are mainly in the first singlet excited state (S 1 ) state, and the excitons that can transfer to the CT state are very limited. Thus, the UV light-induced afterglow is much weaker than the X-ray-induced afterglow. This hypothesis was confirmed by photoconductive gain measurements. As shown in Fig. 3e and Supplementary Figs. 17-18, the electrical conductivities of both TPP-3C2B:DMA and TPP-3C2B barely change under UV light but significantly increase under X-ray irradiation, demonstrating that the carrier formation quantity under X-ray irradiation is much greater than that under UV light. The above results demonstrate that carriers stored in the CT state can be released and form triplet excitons via the TADP process, which provides a new pathway for increasing the XEL of organic scintillators. The above conclusion was further confirmed by temperature-dependent radioluminescence measurements. As shown in Fig. 3f and Supplementary Figs. 19 and 20, TPP-3C2B and TPP-3C2B:DMA exhibit intense and almost the same XEL at 83 K. With an increase in temperature, the XEL of TPP-3C2B rapidly decreases, while the XEL of TPP-3C2B:DMA slowly decreases. At 293 K, the XEL of TPP-3C2B is only 4% of that at 83 K, while the XEL of TPP-3C2B:DMA is 20% of that at 83 K. The similar intense XEL at 83 K can be attributed to the restriction of intramolecular motion by the low temperature, which blocks the nonradiative transition channel. With an increase in temperature, thermal motion significantly quenches the emission. Meanwhile, the TADP process leads to an increase in phosphorescence and slows the decrease in XEL. For TPP-3C2B, there is only an unstable intra-CT state at 120 K, while for TPP-3C2B:DMA, the inter-CT state is stable at all temperatures. Therefore, the reduction in XEL for TPP-3C2B:DMA with increasing temperature is much slower than that for TPP-3C2B. The same result can be obtained by temperature-dependent photoluminescence measurements (Supplementary Figs. 21-22). These results demonstrate that the TADP induced by the CT state can significantly increase the XEL of organic scintillators. The suggested mechanism is further validated by results obtained through density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies. These calculations reveal that due to the significant spin-orbit coupling effect, singlet excitons show a preference for transitioning to the triplet energy surface 35,36 . Supplementary Table 3 displays the spin-orbit coupling matrix elements (SOCMEs), which measure 142.23 and 1115.30 cm -1 for the S 1 and the two lowest triplet excited states, T 1 and T 2 , respectively. Moreover, as displayed in Fig. 3g, both singlet and triplet excitation processes occur on the TPP-3C2B moiety, indicating that spin-crossover is mainly driven by TPP-3C2B rather than DMA. Notably, for the dopant-free system of TPP-3C2B, the spin density of the triplet state is mainly distributed across TPP-3C2B, and Mulliken charge/spin population analysis reveals the intra-CT state. However, when the electron-donating moiety of DMA is involved, the spin density is prone to localize on the TPP-3C2B and DMA partners, which present an inter-CT property (Figs. 3h-i, Supplementary Fig. 23 and Supplementary Tables 4-5). With these diabatic states established, the energy gap between the first triplet excited state and the CT state, denoted Δ E TCT , is calculated to be 0.32 eV (Fig. 3d). The calculated Δ E TCT is fitted well with the experimental depth of the CT state trap (0.37 eV). This gap is sufficiently small to facilitate the TADP process, which in turn corroborates the proposed luminescence mechanism 37 . X-ray and afterglow imaging Based on the excellent scintillation performance and long afterglow properties of TPP-3C2B:DMA, a portable large-area flexible organic scintillator screen was constructed by combining this material with flexible substrates (polydimethylsiloxane, PDMS). The scintillator screen has excellent folding, bending and stretching properties, is easy to carry, and can be prepared at different sizes according to the imaging target (Fig. 4a). As shown in Fig. 4b and Supplementary Fig. 24, stress-strain testing reveals that the maximum tensile deformation of the screen can reach 99% of its own size, and the screen can be cyclically stretched more than 100 times. In addition, when the scintillator screen stretching/bending cycle is repeated 1000 times, the XEL performance remains almost unchanged (Fig. 4c and Supplementary Fig. 25). The scintillator screen is highly hydrophobic and has a contact angle of 117° between the film surface and water droplets. Therefore, the XEL intensity of the scintillator screen is unaffected even after it is directly exposed to a large area of water (Supplementary Fig. 26). To explore the imaging performance of the scintillator screen, a simple X-ray imaging device was constructed (Supplementary Fig. 4). As shown in Supplementary Fig. 27, the resolution of the scintillator screen can reach 20 lp mm -1 (25 mm). Under X-ray irradiation, the inbuilt refill of a ballpoint pen, the tiny roots of sycamore leaves and the complex circuits inside a radiation dose alarm can be clearly displayed on the scintillator screen (Supplementary Fig. 28). In addition, the scintillator screen was used to simulate industrial flaw detection in computer mice and circuit switches with damaged internal wiring. As shown in Figs. 4d-e, the internal structure and damage information of a computer mouse and a circuit switch can be recorded on the scintillator screen. More importantly, the scintillator screen was successfully used for X-ray afterglow imaging at room temperature. As shown in Fig. 4f and Supplementary Videos 2-4, X-ray can be used to store images of metal artefact, capacitor encapsulated in capsule, and melon seed on the scintillation screen for up to 20 min. Compared with inorganic afterglow scintillator screens, which release the stored images at high temperatures 32 , the organic scintillator screen is the first scintillator screen with a room-temperature X-ray afterglow imaging property. Summary In conclusion, a highly stable CT state trap was constructed in a D-A-doped AIE organic scintillator, leading to a unique TADP process under X-ray irradiation. These features allow the organic scintillator to capture and convert high-energy carriers more efficiently, significantly enhancing the exciton generation efficiency. As a result, ultrahigh LY and X-ray afterglow imaging at room temperature are realized. This work demonstrates that improvement of the capture and conversion of high-energy carriers is a brand-new strategy for the design of high-performance organic scintillators. Declarations Acknowledgements This work was supported by the National Natural Science Foundation of China (92061201, 22371264). Author contributions # These authors contributed equally to this work. Q. C. P., Y. B. S., K. L., S. Q. Z. and B. Z. T. conceived this study. Q. C. P., Y. B. S., K. L., S. Q. Z. and B. Z. T. designed the experiments. Q. C. P., Y. B. S., Q. Y., J. W. Y., Z. Y. G., Y. Z. and K. L. carried out the experiments and data analysis. S. Q. Z. supervised the research. All the authors interpreted the results, and Q. C. P., K. L., Y. B. S., S. Q. Z. and B. Z. T. cowrote the manuscript with input from all the authors. Competing interests The authors declare no competing interests. Additional information Supplementary information is available for this paper. Correspondence and requests for materials should be addressed to XX. Reprints and permissions information is available at www.nature.com/reprints. References Joo, W. J. et al. Metasurface-driven OLED displays beyond 10000 pixels per inch. Science 370 , 459-463 (2020). Kim, M. H. et al. 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Tang","email":"","orcid":"https://orcid.org/0000-0002-0293-964X","institution":"The Chinese University of Hong Kong, Shenzhen","correspondingAuthor":false,"prefix":"","firstName":"Ben","middleName":"Zhong","lastName":"Tang","suffix":""}],"badges":[],"createdAt":"2024-02-01 10:01:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3916923/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3916923/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":50935124,"identity":"8864cb8d-7fb5-4fb7-9f21-ed4a065d7e42","added_by":"auto","created_at":"2024-02-09 20:29:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":313302,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic diagram of the mechanism and molecular structure. a,\u003c/strong\u003e Schematic diagram of the XEL process of TPP-3C2B:DMA. \u003cstrong\u003eb,\u003c/strong\u003e Single-crystal structure of TPP-3C2B:DMA. \u003cstrong\u003ec, \u003c/strong\u003ePXRD data of TPP-3C2B:DMA and TPP-3C2B.\u003cstrong\u003e d,\u003c/strong\u003e Synthesis route of TPP-3C2B:DMA crystals.\u003cstrong\u003e e,\u003c/strong\u003e Photographs of a TPP-3C2B:DMA crystal in bright (left) and dark (right) fields.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/d3d4dfb24c41baa5f49f8d20.png"},{"id":50935125,"identity":"ada47f77-b1ea-491d-9eb6-b37fc3c32aa0","added_by":"auto","created_at":"2024-02-09 20:29:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":341360,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of the scintillation properties of TPP-3C2B:DMA. a,\u003c/strong\u003e Histogram of the XEL intensities of TPP-3C2B:DMA and commercial scintillators. \u003cstrong\u003eb\u003c/strong\u003e-\u003cstrong\u003ec,\u003c/strong\u003e Variation in the X-ray attenuation efficiency with the X-ray energy and sample thickness. \u003cstrong\u003ed,\u003c/strong\u003e XEL spectra of TPP-3C2B:DMA and BGO with the same thickness and cross-sectional area (thickness = 0.5 mm). \u003cstrong\u003ee\u003c/strong\u003e, XEL spectra of TPP-3C2B:DMA at different X-ray doses. \u003cstrong\u003ef,\u003c/strong\u003e Dose rate dependence of the XEL intensity of TPP-3C2B:DMA. \u003cstrong\u003eg,\u003c/strong\u003e Cyclic stability of TPP-3C2B:DMA under high-dose X-ray irradiation (278 μGy s\u003csup\u003e-1\u003c/sup\u003e). \u003cstrong\u003eh\u003c/strong\u003e-\u003cstrong\u003ei,\u003c/strong\u003e Afterglow photograph and attenuation curve of TPP-3C2B:DMA after X-ray excitation was stopped.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/40da0c03601579926814fe11.png"},{"id":50935577,"identity":"60132e79-fde2-486b-a0a5-7f68831dc1b7","added_by":"auto","created_at":"2024-02-09 20:37:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":263991,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of the scintillation mechanism of TPP-3C2B:DMA. a, \u003c/strong\u003eTime-dependent emission decay curves of TPP-3C2B:DMA at different temperatures after X-ray excitation was stopped. Inset: The curves were fitted with second-order reaction dynamics to calculate the rate constants (\u003cem\u003ek\u003c/em\u003e). \u003cstrong\u003eb,\u003c/strong\u003e The rate constants\u003cstrong\u003e \u003c/strong\u003ewere fitted with Arrhenius expressions. \u003cstrong\u003ec,\u003c/strong\u003e Afterglow intensity of TPP-3C2B:DMA after X-ray irradiation with thermal stimulation. The samples were excited with an X-ray source at 50 kV for 200 s, after which the curves were recorded. \u003cstrong\u003ed,\u003c/strong\u003e Energy diagram and photophysical processes of TPP-3C2B:DMA after excitation. \u003cstrong\u003ee,\u003c/strong\u003e Current-voltage curves of TPP-3C2B:DMA under dark UV light and X-ray irradiation. \u003cstrong\u003ef,\u003c/strong\u003e Temperature-dependent XEL intensity of TPP-3C2B:DMA and TPP-3C2B at 510 nm. \u003cstrong\u003eg,\u003c/strong\u003e Schematic representation of the intersystem crossing in TPP-3C2B:DMA starting from the ground state and the electron density distributions of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). \u003cstrong\u003eh,\u003c/strong\u003e QM/MM model of TPP-3C2B:DMA. \u003cstrong\u003ei\u003c/strong\u003e. Spin density localized on the \u003csup\u003e3\u003c/sup\u003eTPP-3C2B pair (left) and \u003csup\u003e3\u003c/sup\u003eTPP-3C2B:DMA moieties (right) (isovalue=0.001).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/b24afb59b9d08592f32f474c.png"},{"id":50935129,"identity":"32a2d19c-70ce-4611-b397-9c4e5e1a04d3","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":481873,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eHigh-resolution X-ray and afterglow imaging using a TPP-3C2B:DMA scintillator screen. a, \u003c/strong\u003ePortable large-area flexible scintillator screen. \u003cstrong\u003eb,\u003c/strong\u003e Stress-strain test curve (clamping distance = 15 mm, tensile rate = 2 mm min\u003csup\u003e-1\u003c/sup\u003e, tensile strength = 0.6 MPa).\u003cstrong\u003e c\u003c/strong\u003e, Stretching and bending of the scintillator screen. \u003cstrong\u003ed\u003c/strong\u003e-\u003cstrong\u003ee\u003c/strong\u003e, X-ray detection of internal damage for a computer mouse and a circuit switch using the scintillator screen. \u003cstrong\u003ef, \u003c/strong\u003eX-ray afterglow imaging of different objects, with a recorded time ranging from 0.5 min to 20 min.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/05a910e77ee8b7e1db257d3f.png"},{"id":72898298,"identity":"6479daf5-d5bd-48cd-b3f3-9850ab5ea632","added_by":"auto","created_at":"2025-01-03 12:18:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1852820,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/e01610f8-228f-4a86-852e-0a5b2894e553.pdf"},{"id":50935123,"identity":"5a8700f1-c81f-4a14-b032-85d535f3603c","added_by":"auto","created_at":"2024-02-09 20:29:26","extension":"cif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1422293,"visible":true,"origin":"","legend":"Extended Data 1","description":"","filename":"TPP3C2B.cif","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/2d971fc49634d04821783dc8.cif"},{"id":50935122,"identity":"acea6515-af55-4d54-97a0-e47b97fff1c0","added_by":"auto","created_at":"2024-02-09 20:29:26","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":82398,"visible":true,"origin":"","legend":"Extended Data 2","description":"","filename":"checkcifTPP3C2B.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/45fb3da291ca5eafbb4aa4f7.pdf"},{"id":50935130,"identity":"741faa7e-2179-488d-b3c5-df7de36284e9","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"cif","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1656069,"visible":true,"origin":"","legend":"Extended Data 3","description":"","filename":"TPP3C2BDMA.cif","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/c449ea4cad6250533c84e4d8.cif"},{"id":50935127,"identity":"86656971-930f-4473-8093-56ea7d5ec34d","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"pdf","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":83596,"visible":true,"origin":"","legend":"Extended Data 4","description":"","filename":"checkcifTPP3C2BDMA.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/fd8ad132c8618633da1bf630.pdf"},{"id":50935131,"identity":"39a67651-bc67-4e24-b1e5-1d8001494118","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"mp4","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":14169572,"visible":true,"origin":"","legend":"\u003cp\u003eVideo 1\u003c/p\u003e","description":"","filename":"Video1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/4f9a42094262613cd48c8358.mp4"},{"id":50935133,"identity":"44c0814c-4c79-4d1a-9c8c-396a8f490162","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"mp4","order_by":6,"title":"","display":"","copyAsset":false,"role":"supplement","size":5095390,"visible":true,"origin":"","legend":"\u003cp\u003eVideo 2\u003c/p\u003e","description":"","filename":"Video2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/de64260115bbfb8925330672.mp4"},{"id":50935134,"identity":"6ad0747c-ed12-45f6-896e-c387546a14de","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"mp4","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":2963047,"visible":true,"origin":"","legend":"\u003cp\u003eVideo 3\u003c/p\u003e","description":"","filename":"Video3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/e496fb6f9b066da7f7ee2356.mp4"},{"id":50935132,"identity":"90366cc1-01f9-46cd-95bb-5a8e0de0996d","added_by":"auto","created_at":"2024-02-09 20:29:27","extension":"mp4","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":1562381,"visible":true,"origin":"","legend":"\u003cp\u003eVideo 4\u003c/p\u003e","description":"","filename":"Video4.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/b41f03bb994380051ebf8692.mp4"},{"id":50935135,"identity":"bd393361-6f06-463b-a2d0-93454bb494ec","added_by":"auto","created_at":"2024-02-09 20:29:28","extension":"docx","order_by":9,"title":"","display":"","copyAsset":false,"role":"supplement","size":2492564,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary Information\u003c/p\u003e","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3916923/v1/8332d7f6564892ea3e659081.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"CT state carrier storage-triggered TADP in an organic scintillator","fulltext":[{"header":"Main text","content":"\u003cp\u003eIn recent years, X-ray detection technology has received increasing attention in various fields, such as high-energy physics, medical diagnosis, and nondestructive testing\u003csup\u003e11-15\u003c/sup\u003e. As the core material of X-ray detection technology, scintillators directly determine the detection performance and have become the most important optoelectronic material in X-ray detection technology\u003csup\u003e16-21\u003c/sup\u003e. At present, the mainstream research hotspot of scintillators is inorganic semiconductors and inorganic-organic hybrid materials due to their high light yield (LY) and multiple luminescence properties\u003csup\u003e22-26\u003c/sup\u003e. However, harsh preparation conditions and poor stability usually lead to high usage costs for traditional scintillators. Moreover, the heavy metals contained in these scintillators pose a potential environmental pollution risk, greatly limiting their popularity and application. Small-molecule organic materials have many advantages, such as heavy metal-free constituents, synthesis designability, affordable raw materials, and low usage costs\u003csup\u003e1-6\u003c/sup\u003e. These materials have achieved great success in optoelectronic fields, including in organic light-emitting diodes (OLEDs), photovoltaic devices and field-effect transistors, which means that they have broad development potential in the field of scintillators.\u003c/p\u003e\n\u003cp\u003eIn fact, the scintillation behaviour of small-molecule organic materials under X-ray irradiation was discovered for anthracene crystals as early as 1947\u003csup\u003e27\u003c/sup\u003e. However, the development of organic scintillators has been very slow over the past several decades. The X-ray excited luminescence (XEL) mechanism of an organic scintillator is shown in Fig. 1a, which can be divided into three stages\u003csup\u003e28,29\u003c/sup\u003e. In the first stage (\u003cstrong\u003eStep I\u003c/strong\u003e), high-energy X-ray is absorbed by atoms through the photoelectric effect and Compton scattering to produce high-energy electrons. In the second stage\u0026nbsp;(\u003cstrong\u003eStep II\u003c/strong\u003e), through inelastic electron scattering and the Auger effect, some of the high-energy electrons\u0026nbsp;produce secondary electrons and holes, which interact to produce excitons. In the third stage (\u003cstrong\u003eStep III\u003c/strong\u003e), visible luminescence is produced by the radiative transition process of the excitons.\u0026nbsp;Because of the lack of heavy atoms, most organic scintillators exhibit weak X-ray absorption, and the spin-forbidden transition from the triplet excited state to the singlet ground state limits their exciton utilization. In recent years, heavy atoms such as bromine and iodine have been added to organic scintillators to increase their X-ray absorption, while fast thermally activated up-conversion processes and aggregation-induced emission (AIE) moieties have been introduced into the design of organic scintillators to increase exciton utilization\u003csup\u003e7-10\u003c/sup\u003e. However, very few of these materials have conspicuous scintillation properties, and the LY of most small-molecule organic materials is far less than that of inorganic materials. The cause of the above results is that in \u003cstrong\u003eStep II\u003c/strong\u003e, many high-energy electrons with inappropriate energy cannot effectively produce secondary electrons and holes. To solve this problem, a donor-acceptor (D-A)-doped AIE system of TPP-3C2B:DMA is prepared in this work, which constructs a charge transfer (CT) state trap to capture high-energy electrons. The triplet-triplet energy transfer (TTET) leads to a unique thermally activated delayed phosphorescence (TADP) process, providing a new pathway for significantly enhancing the exciton generation efficiency, resulting in an ultrahigh LY. Moreover, the presence of a CT state trap endows the organic scintillator with ultralong afterglow at room temperature, realizing X-ray afterglow imaging.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis and characterization of scintillation properties\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTPP-3C2B:DMA was easily prepared by cocrystallization of TPP-3C2B and DMA\u003csup\u003e30\u003c/sup\u003e. The doping ratio of DMA was 0.5%, which could not be determined by single-crystal X-ray diffraction (SCXRD) or powder X-ray diffraction (PXRD) (Figs. 1b-c) but could be confirmed by \u003csup\u003e1\u003c/sup\u003eH-NMR (Supplementary Figs. 5-6).\u0026nbsp;The preparation method of TPP-3C2B:DMA crystals is very mild and simple, and gram-scale preparation of millimetre-scale crystals can be easily achieved under laboratory conditions (Figs. 1d-e). TPP-3C2B:DMA has a strong XEL under X-ray excitation. As shown in Fig. 2a, its XEL intensity not only far exceeds that of the plastic organic scintillator EJ-200 and the classical organic scintillator anthracene but also surpasses that of many commercially available inorganic scintillators, such as Bi\u003csub\u003e4\u003c/sub\u003eGe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e (BGO). Next, using BGO as a standard sample, according to the curves of the X-ray attenuation efficiency with the X-ray energy and sample thickness (Figs. 2b-c) and the XEL spectral integral area ratio of TPP-3C2B:DMA to BGO (Fig. 2d and Supplementary Fig. 7), the relative LY of TPP-3C2B:DMA can be calculated as 76600 photon MeV\u003csup\u003e-1\u003c/sup\u003e, which is currently the highest reported LY of organic scintillators. In medical applications, the X-ray dose should be as low as possible to minimize harm to the human body while ensuring completion of detection. As shown in Figs. 2e-f, TPP-3C2B:DMA has an ultrasensitive response to X-ray, and its XEL intensity presents a good linear relationship with the X-ray dose. The lowest detection limit of TPP-3C2B:DMA calculated by the 3s\u0026nbsp;method is 12.3 nGy s\u003csup\u003e-1\u003c/sup\u003e, which is far lower than the minimum dose requirement for medical detection (5.5\u0026nbsp;mGy s\u003csup\u003e-1\u003c/sup\u003e)\u003csup\u003e31\u003c/sup\u003e. In addition, for scintillators, stable cycling performance is also a very important usage indicator. As shown in Fig. 2g, TPP-3C2B:DMA can still well maintain its XEL intensity after being continuously exposed to high-dose X-ray (278 \u0026mu;Gy s\u003csup\u003e-1\u003c/sup\u003e) for 60 min or after cycling on and off 60 times. Most importantly, TPP-3C2B:DMA can exhibit a significant 7-hour afterglow observable by the naked eye and a time curve after stopping the 50 kV X-ray excitation (Figs. 2h-i and Supplementary Video 1), which is the first ultralong afterglow observed for a small-molecule organic material under X-ray excitation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInvestigation of the scintillation mechanism\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo understand the influence of the CT state on the LY and afterglow of TPP-3C2B:DMA, undoped TPP-3C2B was selected as a control compound. As shown in Supplementary Figs. 8-10, the LY of TPP-3C2B is much lower than that of TPP-3C2B:DMA, although the photoluminescence intensity of the former is still 40% that of the latter. The X-ray absorbance capacity of TPP-3C2B is almost the same as that of TPP-3C2B:DMA (Supplementary Fig. 11), which means that \u003cstrong\u003estep I\u003c/strong\u003e is not the origin of their different XEL properties. Moreover, TPP-3C2B and TPP-3C2B:DMA have almost the same crystal structure (Figs. 1b-c and Supplementary\u0026nbsp;Fig. 12), ensuring their similar nonradiative transition processes induced by molecular packing. That is, the influence of \u003cstrong\u003estep III\u003c/strong\u003e on their different XEL properties can also be excluded. Thus, the difference in LY between TPP-3C2B and TPP-3C2B:DMA is mainly attributed to the ability of the CT state to capture electrons and holes.\u003c/p\u003e\n\u003cp\u003eAs shown in Supplementary Fig. 13, there are two lifetimes in TPP-3C2B, 0.3 \u0026mu;s and 74 ms, corresponding to thermally activated delayed fluorescence (TADF) and phosphorescence, respectively. For TPP-3C2B:DMA, three lifetimes are observed, 3.3 \u0026mu;s, 310 ms and 7 h,\u0026nbsp;corresponding to TADF, TADP and afterglow, respectively. The origin of the afterglow was investigated by time-dependent emission decay measurements at different temperatures. As shown in Fig. 3a, the afterglow decay curves can be well fit with second-order reaction kinetics (1/\u003cem\u003eI\u003c/em\u003e \u0026micro;\u003cem\u003e\u0026nbsp;\u003c/em\u003et), suggesting that the generation of\u0026nbsp;excitons is a second-order kinetics process. This result is obtained because the recombination process occurs between electrons and holes and because the concentrations of electrons and holes are equal; thus, the reaction rate should be proportional to the square of the electron concentration (or hole concentration), i.e., a second-order reaction. This result demonstrates that the CT state can effectively capture and store carriers, which is the origin of the intense XEL.\u003c/p\u003e\n\u003cp\u003eFurthermore, the activation energy (\u003cem\u003eE\u003csub\u003ea\u003c/sub\u003e\u003c/em\u003e), i.e., the depth of the CT state trap, can be evaluated according to the Arrhenius expression:\u003c/p\u003e\n\u003cp\u003eln\u003cem\u003ek\u003c/em\u003e = -\u003cem\u003eE\u003csub\u003ea\u003c/sub\u003e\u003c/em\u003e/RT + constant\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(1)\u003c/p\u003e\n\u003cp\u003ewhere T is the temperature and R is the ideal gas constant. The depth of the CT state trap is calculated to be 35.5 kJ mol\u003csup\u003e-1\u003c/sup\u003e (0.37 eV) (Fig. 3b). As shown in Supplementary Fig. 14, the same result can be obtained by fitting the photoluminescence decay curves, demonstrating that the photoexcited afterglow and X-ray excited afterglow have the same source, that is, the TADP from the CT state to the first excited triplet state (T\u003csub\u003e1\u003c/sub\u003e).\u003c/p\u003e\n\u003cp\u003eThe afterglow of TPP-3C2B:DMA and TPP-3C2B with changing temperature was further investigated\u003csup\u003e32,33\u003c/sup\u003e. The samples were irradiated by X-ray at 83 K. When the X-ray was shut off, the emission intensity at 510 nm was recorded, and the temperature was gradually increased from 83 K to room temperature (Fig. 3c). As shown, only a very short afterglow can be observed at 83 K, which originates from the enhanced phosphorescence at low temperatures. When the temperature is increased, intense afterglow emerges and reaches a maximum at 120 K. Interestingly, when the temperature is further increased, the afterglow quickly disappears for TPP-3C2B, while a new afterglow peak emerges for TPP-3C2B:DMA at 150 K that reaches a maximum at 220 K. A proposed mechanism for these phenomena is shown in Fig. 3d and Supplementary Fig. 15. For TPP-3C2B, there is an intramolecular CT (intra-CT) state derived from the charge transfer between the Br\u003csup\u003e-\u0026nbsp;\u003c/sup\u003eand phosphonium cations\u003csup\u003e30,34\u003c/sup\u003e. Carriers produced by X-ray irradiation are stored in the intra-CT state of TPP-3C2B at 83 K. With an increase in temperature, a TADP process occurs, and visible afterglow emerges. However, because the intra-CT state is unstable at high temperatures, the afterglow quickly disappears when the temperature is further increased. In contrast, there is another intermolecular CT (inter-CT) state in addition to the intra-CT state for TPP-3C2B:DMA, and the depth of the inter-CT state trap is deeper than that of the intra-CT state. As a result, TPP-3C2B:DMA and TPP-3C2B exhibit almost the same afterglow change at 83 K-120 K. When the temperature is further increased, the carriers stored in the inter-CT state are activated, and exciton formation reaches a maximum at 220 K. At room temperature, this TADP process is maintained, resulting in visible afterglow. Under UV light, similar afterglow changes can be observed for TPP-3C2B:DMA and TPP-3C2B (Supplementary\u0026nbsp;Fig. 16). However, the excitons produced by UV light irradiation are mainly in the first singlet excited state (S\u003csub\u003e1\u003c/sub\u003e) state, and the excitons that can transfer to the CT state are very limited. Thus, the UV light-induced afterglow is much weaker than the X-ray-induced afterglow. This hypothesis was confirmed by photoconductive gain measurements. As shown in Fig. 3e and Supplementary Figs. 17-18, the electrical conductivities of both TPP-3C2B:DMA and TPP-3C2B barely change under UV light but significantly increase under X-ray irradiation, demonstrating that the carrier formation quantity under X-ray irradiation is much greater than that under UV light. The above results demonstrate that carriers stored in the CT state can be released and form triplet excitons via the TADP process, which provides a new pathway for increasing the XEL of organic scintillators.\u003c/p\u003e\n\u003cp\u003eThe above conclusion was further confirmed by temperature-dependent radioluminescence measurements. As shown in Fig. 3f and\u0026nbsp;Supplementary Figs. 19 and 20, TPP-3C2B and TPP-3C2B:DMA exhibit intense and almost the same XEL at 83 K. With an increase in temperature, the XEL of TPP-3C2B rapidly decreases, while the XEL of TPP-3C2B:DMA slowly decreases. At 293 K, the XEL of TPP-3C2B is only 4% of that at 83 K, while the XEL of TPP-3C2B:DMA is 20% of that at 83 K. The similar intense XEL at 83 K can be attributed to the restriction of intramolecular motion by the low temperature, which blocks the nonradiative transition channel. With an increase in temperature, thermal motion significantly quenches the emission. Meanwhile, the TADP process leads to an increase in phosphorescence and slows the decrease in XEL. For TPP-3C2B, there is only an unstable intra-CT state at 120 K, while for TPP-3C2B:DMA, the inter-CT state is stable at all temperatures. Therefore, the reduction in XEL for TPP-3C2B:DMA with increasing temperature is much slower than that for TPP-3C2B. The same result can be obtained by temperature-dependent photoluminescence measurements (Supplementary Figs. 21-22). These results demonstrate that the TADP induced by the CT state can significantly increase the XEL of organic scintillators.\u003c/p\u003e\n\u003cp\u003eThe suggested mechanism is further validated by results obtained through density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies. These calculations reveal that due to the significant spin-orbit coupling effect, singlet excitons show a preference for transitioning to the triplet energy surface\u003csup\u003e35,36\u003c/sup\u003e. Supplementary\u0026nbsp;Table 3 displays the spin-orbit coupling matrix elements (SOCMEs), which measure 142.23 and 1115.30 cm\u003csup\u003e-1\u003c/sup\u003e for the S\u003csub\u003e1\u003c/sub\u003e and the two lowest triplet excited states, T\u003csub\u003e1\u003c/sub\u003e and T\u003csub\u003e2\u003c/sub\u003e, respectively. Moreover, as displayed in Fig. 3g, both singlet and triplet excitation processes occur on the TPP-3C2B moiety, indicating that spin-crossover is mainly driven by TPP-3C2B rather than DMA. Notably, for the dopant-free system of TPP-3C2B, the spin density of the triplet state is mainly distributed across TPP-3C2B, and Mulliken charge/spin population analysis reveals the intra-CT state. However, when the electron-donating moiety of DMA is involved, the spin density is prone to localize on the TPP-3C2B and DMA partners, which present an inter-CT property (Figs. 3h-i, Supplementary Fig. 23 and Supplementary Tables 4-5). With these diabatic states established, the energy gap between the first triplet excited state and the CT state, denoted \u0026Delta;\u003cem\u003eE\u003c/em\u003e\u003csub\u003eTCT\u003c/sub\u003e, is calculated to be 0.32 eV (Fig. 3d). The calculated \u0026Delta;\u003cem\u003eE\u003c/em\u003e\u003csub\u003eTCT\u0026nbsp;\u003c/sub\u003eis fitted well with the experimental depth of the CT state trap (0.37 eV). This gap is sufficiently small to facilitate the TADP process, which in turn corroborates the proposed luminescence mechanism\u003csup\u003e37\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eX-ray and afterglow imaging\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBased on the excellent scintillation performance and long afterglow properties of TPP-3C2B:DMA, a portable large-area flexible organic scintillator screen was constructed by combining this material with flexible substrates (polydimethylsiloxane, PDMS). The scintillator screen has excellent folding, bending and stretching properties, is easy to carry, and can be prepared at different sizes according to the imaging target (Fig. 4a). As shown in Fig. 4b and Supplementary Fig. 24, stress-strain testing reveals that the maximum tensile deformation of the screen can reach 99% of its own size, and the screen can be cyclically stretched more than 100 times. In addition, when the scintillator screen stretching/bending cycle is repeated 1000 times, the XEL performance remains almost unchanged (Fig. 4c and\u0026nbsp;Supplementary Fig. 25). The scintillator screen is highly hydrophobic and has a contact angle of 117\u0026deg; between the film surface and water droplets. Therefore, the XEL intensity of the scintillator screen is unaffected even after it is directly exposed to a large area of water (Supplementary Fig. 26).\u003c/p\u003e\n\u003cp\u003eTo explore the imaging performance of the scintillator screen, a simple X-ray imaging device was constructed\u0026nbsp;(Supplementary Fig. 4). As shown in Supplementary\u0026nbsp;Fig. 27, the\u0026nbsp;resolution of the scintillator screen can reach 20 lp mm\u003csup\u003e-1\u003c/sup\u003e (25 mm). Under X-ray irradiation, the inbuilt refill of a ballpoint pen, the tiny roots of sycamore leaves and the complex circuits inside a radiation dose alarm can be clearly displayed on the scintillator screen (Supplementary Fig. 28). In addition, the scintillator screen was used to simulate industrial flaw detection in computer mice and circuit switches with damaged internal wiring. As shown in Figs. 4d-e, the internal structure and damage information of a computer mouse and a circuit switch can be recorded on the scintillator screen. More importantly, the scintillator screen was successfully used for X-ray afterglow imaging at room temperature. As shown in Fig. 4f and Supplementary Videos 2-4, X-ray can be used to store images of metal artefact, capacitor encapsulated in capsule, and melon seed on the scintillation screen for up to 20 min. Compared with inorganic afterglow scintillator screens, which release the stored images at high temperatures\u003csup\u003e32\u003c/sup\u003e, the organic scintillator screen is the first scintillator screen with a room-temperature X-ray afterglow imaging property.\u003c/p\u003e"},{"header":"Summary","content":"\u003cp\u003eIn conclusion, a highly stable CT state trap was constructed in a D-A-doped AIE organic scintillator, leading to a unique TADP process under X-ray irradiation. These features allow the organic scintillator to capture and convert high-energy carriers more efficiently, significantly enhancing the exciton generation efficiency. As a result, ultrahigh LY and X-ray afterglow imaging at room temperature are realized. This work demonstrates that improvement of the capture and conversion of high-energy carriers is a brand-new strategy for the design of high-performance organic scintillators.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National Natural Science Foundation of China (92061201, 22371264).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e#\u003c/sup\u003eThese authors contributed equally to this work. Q. C. P., Y. B. S., K. L., S. Q. Z. and B. Z. T. conceived this study. Q. C. P., Y. B. S., K. L., S. Q. Z. and B. Z. T. designed the experiments. Q. C. P., Y. B. S., Q. Y., J. W. Y., Z. Y. G., Y. Z. and K. L. carried out the experiments and data analysis. S. Q. Z. supervised the research. All the authors interpreted the results, and Q. C. P., K. L., Y. B. S., S. Q. Z. and B. Z. T. cowrote the manuscript with input from all the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary information is available for this paper.\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials should be addressed to XX.\u003c/p\u003e\n\u003cp\u003eReprints and permissions information is available at www.nature.com/reprints.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eJoo, W. J. et al. Metasurface-driven OLED displays beyond 10000 pixels per inch. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e370\u003c/strong\u003e, 459-463 (2020).\u003c/li\u003e\n\u003cli\u003eKim, M. H. et al. 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Crossover from single-step tunneling to multistep hopping for molecular triplet energy transfer. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e328\u003c/strong\u003e, 1547-1550 (2010).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3916923/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3916923/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOrganic scintillators are among the most promising scintillators due to their inherent merits in terms of heavy metal-free constituents, synthesis designability, affordability of raw materials, and low usage costs\u003csup\u003e1-6\u003c/sup\u003e. However, the limited X-ray excited luminescence (XEL) property of organic scintillators affects their application. To date, the main approaches for improving the XEL property of organic scintillators have focused on introducing heavy atoms to increase the absorbance of X-ray and establishing new luminescence pathways, such as thermally activated delayed fluorescence (TADF), to increase the exciton utilization efficiency\u003csup\u003e7-10\u003c/sup\u003e. Even so, the XEL property of organic scintillators is not ideal compared with that of commercial inorganic scintillators. In this work, a highly stable charge transfer (CT) state trap was introduced into the design of an organic scintillator. Combined with a unique thermally activated delayed phosphorescence (TADP) process, highly efficient capture and conversion of high-energy carriers are realized. As a result, the exciton generation efficiency dramatically increases, with an ultrahigh light yield (LY), and X-ray afterglow imaging at room temperature is achieved for the first time. This work provides a brand-new strategy for the design of high-performance organic scintillators.\u003c/p\u003e","manuscriptTitle":"CT state carrier storage-triggered TADP in an organic scintillator","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-09 20:29:22","doi":"10.21203/rs.3.rs-3916923/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b5497d1b-6a2a-48b8-956a-0c760361d8f9","owner":[],"postedDate":"February 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":28628204,"name":"Physical sciences/Chemistry/Materials chemistry/Optical materials"},{"id":28628205,"name":"Physical sciences/Chemistry/Physical chemistry/Excited states"}],"tags":[],"updatedAt":"2025-01-04T05:10:21+00:00","versionOfRecord":[],"versionCreatedAt":"2024-02-09 20:29:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3916923","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3916923","identity":"rs-3916923","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}