particles directly determines the performance of time resolution, response rate, and counting ability of radiation detectors. For example, dynamic high speed X-ray imaging requires frame rates of 2 ns (GHz) and thus the scintillator with sub-nanosecond response is in urgent demand. [3] Sub-nanosecond scintillator is also highly needed in PET detector module to increase the accidental coincidence rate, without image reconstruction to approaching the recognized goals of 10 ps time resolution. [2,7,8] Some nuclear physics experiments with very high count rates required sub-nanosecond scintillation to avoid signal piling up. [9] BaF 2 , CsCl, and ZnO:Ga scintillators have demonstrated sub-nanosecond response speed, with the short lifetime as 0.8, 0.9, and 0.7 ns, respectively. [10,11] However, BaF 2 and CsCl suffered from longstanding weakness of extra-low light yield (<1500 photons MeV −1 ) due to the inefficient core-valence transitions and also an undesirable slow lifetime component (few microseconds). [10] Besides the low light yield, ZnO: Ga scintillator was also limited by the manufacturing difficulty in bulk crystal and high production cost. [11,12] Therefore, new sub-nanosecond scintillator materials with considerable light yield urgently need to be explored. Perovskite materials have emerged as a new family of radiation scintillators with tunable wavelength andPerovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub-nanosecond region, while sub-nanosecond scintillators are highly demanded in various radiation detection, including high speed X-ray imaging, time-of-flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb-Br octahedral emitters in 2D organic-inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr 6 ] 2− layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM 2 PbBr 4 . The emitting decay time is shortened as 0.97 ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190 photons MeV −1 , which is greatly higher than conventional ultrafast scintillator BaF 2 (1500 photons MeV −1 ). The rare combination of ultrafast decay time and considerable light yield renders BM 2 PbBr 4 excellent performance in γ-ray, neutron, α-particle detection, and the best theoretical coincidence time resolution of 65.1 ps, which is only half of the reference sample LYSO (141.3 ps).
Lead halide perovskites have recently emerged as promising X/γ-ray scintillators. However, the small Stokes shift of exciton luminescence in perovskite scintillators creates problems for the light extraction efficiency and severely impedes their applications in hard X/γ-ray detection. Dopants have been used to shift the emission wavelength, but the radioluminescence lifetime has also been unwantedly extended. Herein, we demonstrate the intrinsic strain in 2D perovskite crystals as a general phenomenon, which could be utilized as self-wavelength shifting to reduce the self-absorption effect without sacrificing the radiation response speed. Furthermore, we successfully demonstrated the first imaging reconstruction by perovskites for application of positron emission tomography. The coincidence time resolution for the optimized perovskite single crystals (4 × 4 × 0.8 mm3) reached 119 ± 3 ps. This work provides a new paradigm for suppressing the self-absorption effect in scintillators and may facilitate the application of perovskite scintillators in practical hard X/γ-ray detections.
Perovskites are attracting attention for optoelectronic devices. Despite their promise, the large-scale synthesis of perovskite materials with exact stoichiometry, especially high-entropy perovskites, has been a major challenge. Moreover, the difficulty in stoichiometry control also hinders the development of perovskite X-ray flat-panel detectors. Previous reports all employed simple MAPbI 3 as the active layer, while the performance still falls short of optimized single-crystal-based single-pixel detectors. Herein, a scalable and universal strategy of a mechanochemical method is adopted to synthesize stoichiometric high-entropy perovskite powders with high quality and high quantity (>1 kg per batch). By utilizing these stoichiometric perovskites, the first FA 0.9 MA 0.05 Cs 0.05 Pb(I 0.9 Br 0.1 ) 3 -based X-ray flat-panel detector with low trap density and large mobility-lifetime product (7.5 × 10 −3 cm 2 V −1 ) is reported. The assembled panel detector exhibits close-to-single-crystal performance (high sensitivity of 2.1 × 10 4 μC Gy air −1 cm −2 and ultralow detection limit of 1.25 nGy air s −1 ), high spatial resolution of 0.46 lp/pixel, as well as excellent thermal robustness under industrial standards. The high performance in the high-entropy perovskite-based X-ray FPDs has the potential to facilitate the development of new-generation X-ray-detection systems.
Solution-processed polycrystalline perovskite film is promising for the next generation X-ray imaging. However, the spatial resolution of current perovskite X-ray panel detectors is far lower than the theoretical limit. Herein we find that the pixel level non-uniformity, also known as fixed pattern noise (FPN), is the chief culprit affecting the signal-to-noise ratio and reducing the resolution of perovskite detectors. We report a synergistic strategy of rheological engineering the perovskite suspensions to achieve X-ray FPDs with pixel-level high uniformity and near-to-limit spatial resolution. Our approach includes the addition of methylammonium iodide and polyacrylonitrile to the perovskite suspension, to synergistically enhance the flowability and particle stability of the oversaturated solution. The obtained suspension perfectly suits for the blade-coating process, avoiding the uneven distribution of solutes and particles within perovskite films. The assembled perovskite panel detector exhibits greatly improved FPN value (1.39%), high sensitivity (6.3×105 μC Gyair-1 cm−2), low detection limit (14.27 nGyair·s-1) as well as good working stability, close to the performance of single crystal detectors. Most importantly, the detector achieves a resolution of 0.51 lp/pix, exceeding all previous perovskite X-ray flat-panel detectors.
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