Self-wavelength shifting in two-dimensional perovskite for sensitive and fast gamma-ray detection

Scaling Up Purcell-Enhanced Self-Assembled Nanoplasmonic Perovskite Scintillators into the Bulk Regime

Scintillators convert high-energy radiation into detectable photons and play a crucial role in medical imaging and security applications. The enhancement of scintillator performance through nanophotonics and nanoplasmonics, specifically using the Purcell effect, has shown promise but has so far been limited to ultrathin scintillator films because of the localized nature of this effect. This study introduces a method to expand the application of nanoplasmonic scintillators to the bulk regime. By integrating 100-nm-sized plasmonic spheroid and cuboid nanoparticles with perovskite scintillator nanocrystals, nanoplasmonic scintillators are enabled to function effectively within bulk-scale devices. Power and decay rate enhancements of up to (3.20 ± 0.20) and (4.20 ± 0.31) folds are experimentally demonstrated for plasmonic spheroid and cuboid nanoparticles, respectively, in a 5-mm thick CsPbBr3 nanocrystal-polymer scintillator at RT. Theoretical modeling also predicts similar enhancements of up to (2.26 ± 0.31) and (3.02 ± 0.69) folds for the same nanoparticle shapes and dimensions. Moreover, a (2.07 ± 0.39) fold increase in light yield under 241Am γ-excitation is demonstrated. These findings provide a viable pathway for utilizing nanoplasmonics to enhance bulk scintillator devices, advancing radiation detection technology.

Lanthanide-based metal halides prepared at room temperature by recrystallization method for X-ray imaging

Lanthanide (Ln)-based metal halides with excellent luminescence properties, large Stokes shifts, and low toxicity have aroused wide attention as scintillators for X-ray imaging. However, the lack of fast and mild synthesis methods of Ln-based metal halides, as one of the technical challenges, limits their applications. Here, benefiting from the innovative selection of methanol and ethanol as the solvent and anti-solvent, respectively, a series of Cs3LnCl6 (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) microcrystals (MCs) were prepared via the recrystallization method at room temperature for the first time. This recrystallization method could also realize large-scale production at one time and recyclable recrystallization of single-element MCs and the preparation of high-entropy five-element Cs3{TbDyHoErTm}1Cl6 crystals. Among these Cs3LnCl6 MCs, Cs3TbCl6 MCs with 4f → 5d absorption transition possess the highest photoluminescence quantum yield of 90.8%. Besides, under X-ray irradiation, Cs3TbCl6 MCs show a high light yield of ~51,800 photons MeV-1 and the as-fabricated thin films possess promising X-ray imaging ability and excellent spatial resolutions (12 lp mm-1). This work provides a new method for ultrafast preparing Ln-based metal halides under mild synthetic conditions and highlights their excellent potential as scintillators for X-ray imaging.

High-Resolution Flexible X-ray Imaging in a Two-Dimensional Mn2+-Doped Perovskite Scintillator

Flexible scintillator screens characterized by high spatial resolution, low cost, and a simple fabrication process are in significant demand for applications in medical diagnosis and industrial detection. Here, we have demonstrated a new Mn2+-doped two-dimensional (2D) Ruddlesden-Popper type perovskite, (4-tert-butylbenzylamine)2PbBr4:Mn, serving as a highly efficient scintillator candidate. Doping with Mn2+ induces a spin-forbidden internal transition (4T1g → 6A1g) that enhances the energy-transfer efficiency from the strongly bound excitons of the host material to the d electrons of the Mn2+ ions, ultimately leading to intense orange-red emission. This process enhances the photoluminescence quantum yield of (4-tert-butylbenzylamine)2PbBr4 (1) and decreases its self-absorption. Therefore, at the optimal Mn2+-doping concentration, 1:8.4%Mn2+ demonstrates a high light yield of 21,532 Ph/MeV and a low detection limit of 198.19 nGyair s-1, exceeding the performance of a commercial bismuth germanium oxide (BGO) scintillator. Furthermore, we combined ultrafine powders of 1:8.4%Mn2+ with poly(dimethylsiloxane) to fabricate flexible scintillator films. With the optimal film thickness and mass percentage of 1:8.4%Mn2+, the scintillator films achieve their maximum spatial resolution of 17.3 lp mm-1. The above results indicate that the exceptional flexible scintillation imaging performance of 1:8.4%Mn2+ effectively addresses the shortcomings of current commercial scintillators, thereby providing a new option for the scintillator family.

Achieving Efficient Fast Neutron and Gamma Discrimination in Hydrogen-Rich 2D Halide Perovskite Scintillators

Neutron radiation fields frequently coexist with γ-rays, posing a significant challenge to ensure the accuracy of neutron detection. 2D perovskites have been proved to be the potential fast neutron scintillators due to their structural properties and excellent luminescent performance. Herein, the study reports on the scintillation properties of 2D perovskite phenethylammonium lead bromide ((PEA)2PbBr4) single crystal (SC) induced by different types of radiation and first demonstrate its pulse shape discrimination (PSD) capability in neutron/gamma (n/γ) mixed radiation fields. The research has found that the decay time of (PEA)2PbBr4 SC to heavy charged particles (24.4 ns) is significantly faster than that to γ-rays (39.1 ns). This is because the ionization density of heavy charged particles is 2-3 orders of magnitude higher than that of electrons, resulting in a pronounced second-order quenching effect. The unique characteristic endows it with good discrimination capabilities for α-particles and γ-rays. Furthermore, the study has successfully demonstrated a good n/γ discrimination with a figure of merit (FOM) of 0.86 in Deuterium-Deuterium (D-D) fusion reaction. The research not only advances the application of perovskites in the field of neutron detection, but also provides a new alternative for the development of neutron detection technologies.

Structural rigidity, thermochromism and piezochromism of layered hybrid perovskites containing an interdigitated organic bilayer

Layered hybrid perovskites are intensively researched today as highly tunable materials for efficient light harvesting and emitting devices. In classical layered hybrid perovskites, the structural rigidity mainly stems from the crystalline inorganic sublattice, whereas the organic sublattice has a minor contribution to the rigidity of the material. Here, we report two layered hybrid perovskites, (BTa)2PbI4 and (F2BTa)2PbI4, which possess substantially more rigid organic layers due to hydrogen bonding, π-π stacking, and dipole-dipole interactions. These layered perovskites are phase stable under elevated pressures up to 5 GPa and upon temperature lowering down to 80 K. The organic layers, composed of benzotriazole-derived ammonium cations, are among the most rigid in the field of layered hybrid perovskites. We characterize structural rigidity using in situ single-crystal X-ray diffraction during compression up to 5 GPa. Interestingly, the enhanced rigidity of the organic sublattice does not seem to transfer to the inorganic sublattice, leading to an uncommon material configuration with rigid organic layers and deformable inorganic layers. The deformability of the inorganic sublattice is apparent from differences in optical properties between the crystal bulk and surface. Supported by first-principles calculations, we assign these differences to energy transfer processes from the surface to the bulk. The deformability also leads to reversible piezochromism due to shifting of the photoluminescence emission peak with increasing pressure up to 5 GPa, and thermochromism due to narrowing of the photoluminescence emission linewidth with decreasing temperature down to 80 K. This raises the possibility of applying these phase-stable layered hybrid perovskite materials in temperature and/or pressure sensors.

Temperature-Adaptive Organic Scintillators for X-ray Radiography

Organic phosphorescence or thermally activated delayed fluorescence (TADF) scintillators, while effective in utilizing triplet excitons, are sensitive to temperature changes, which can impact radioluminescence performance. In this study, we have developed a type of temperature-adaptive organic scintillator with phosphorescence and TADF dual emission. These scintillators can automatically switch modes with temperature changes, enabling efficient radioluminescence from 77 to 400 K. The highest photoluminescence quantum yield and light yield are 83.2% and 78,229 ± 562 photons MeV-1 excited by a UV lamp and X-ray, respectively. Their detection limit is 51 and 23 nGy·s-1 at room temperature and 77 K, respectively, which is lower than the standard dosage of 5.5 μGy s-1 for X-ray diagnostics. Moreover, given the high spatial resolution of 21.7 l p mm-1, we demonstrate their potential application in multiple-temperature X-ray radiography, offering promising new possibilities. This work opens a new route for developing organic scintillators to adapt to ambient temperature change and paves the way for their use in various temperature-sensitive radiography applications.

Molecular Engineering for High-Performance X-ray Scintillators

X-ray scintillators, materials that convert high-energy radiation into detectable light in the ultraviolet to visible spectrum, are widely used in industrial and medical applications. Organic and organic-inorganic hybrid systems have emerged as promising alternatives for X-ray detection and imaging due to their mechanical flexibility, lightweight, tunable excited states, and solution processability for large-scale fabrication. However, these systems often suffer from weak X-ray absorption and insufficient exciton utilization, which seriously affects their scintillation performance, limiting their potential for broader application and commercialization. This review highlights recent advances in molecular engineering for developing high-performance X-ray scintillators. It focuses on molecular design principles, such as the heavy atom effect, donor-acceptor/host-guest strategies, hydrogen/halogen bonding, molecular sensitization, and crystal packing, for enhancing scintillation performance. By leveraging these approaches, researchers have made significant strides in improving X-ray scintillation efficiency and advancing the potential of these materials for commercial applications.

Improving the Scintillation Performance of PEA2PbBr4 Through Zn2+ and Sb3+ Interstitial Doping Strategy

Organic-inorganic halide 2D perovskite single crystals have recently emerged as promising scintillators for gamma (γ) rays and fast neutrons (nf) detection. However, their energy resolution in γ-rays detection still significantly lags behind that of perovskite semiconductor detectors. Improving crystal defects and enhancing light yield to optimize light output detected by the photomultiplier tube are crucial strategies for addressing this issue. Herein, it is demonstrated that Zn2+ and Sb3+ cation interstitial doping strategy can effectively reduce internal defects within the phenylethylammonium lead bromide (PEA2PbBr4) crystal by regulating lattice expansion. This approach also suppresses light loss caused by exciton-exciton annihilation and accelerates electron-hole recombination processes, optimizing both the luminescence intensity and decay lifetime of the scintillator. The Zn2+ and Sb3+ doping PEA2PbBr4 scintillator achieve an optimal energy resolution of 4.84% and 5.65% at 662 keV for the photopeak, respectively. Additionally, in the 241Am-Be field, effective identification of nf and γ-rays around 1100 keVee is achieved using a pulse shape discrimination (PSD) method, with the figure of merit (FOM) being 0.85 and 1.03, respectively. This work provides a reliable new approach for optimizing the scintillation performance of 2D perovskite and promotes the application of 2D perovskite scintillator in γ-rays and nf detection.

Wide-Bandgap Lead Halide Perovskites for Next-Generation Optoelectronics: Current Status and Future Prospects

Over the past decade, lead halide perovskites (LHPs), an emerging class of organic-inorganic ionic-type semiconductors, have drawn worldwide attention, which injects vitality into next-generation optoelectronics. Facilely tunable bandgap is one of the fascinating features of LHPs, enabling them to be widely used in various nano/microscale applications. Notably, wide-bandgap (WBG) LHPs have been considered as promising alternatives to traditional WBG semiconductors owing to the merits of low-cost, solution processability, superior optoelectronic characteristics, and flexibility, which could improve the cost-effectiveness and expand the application scenarios of traditional WBG devices. Herein, we provide a comprehensive review on the up-to-date research progress of WBG LHPs and their optoelectronics in terms of material fundamentals, optoelectronic devices, and their practical applications. First, the features and shortcomings of WBG LHPs are introduced to objectively display their natural features. Then we separately depict three typical optoelectronic devices based on WBG LHPs, including solar cells, light emitting diodes, and photodetectors. Sequentially, the inspiring applications of these optoelectronic devices in integrated functional systems are elaborately demonstrated. At last, the remaining challenges and future promise of WBG LHPs in optoelectronic applications are discussed. This review highlights the significance of WGB LHPs for promoting the development of the next-generation optoelectronics industry.

Designer bright and fast CsPbBr3 perovskite nanocrystal scintillators for high-speed X-ray imaging

Bright and fast scintillators are highly crucial for high-speed X-ray imaging in the medical diagnostic radiology including angiography and cardiac computed tomography. The CsPbBr3 nanocrystal scintillator featuring a nanosecond radioluminescence decay time is a promising candidate. However, it suffers from a substantial photon self-absorption limiting the light output, and being bright and fast simultaneously is difficult. Here we design and in-situ synthesize multi-site ZnS(Ag)-CsPbBr3 heterostructures to modulate the bright and fast features of scintillators. We find external energy from ZnS(Ag) can effectively transfer to CsPbBr3 based on the non-radiative Förster resonance energy transfer, resulting in a light yield of 40,000 photons MeV-1. By combing a radioluminescence decay time of 36 ns and a spatial resolution of 30 lp mm-1, the scintillator enables high-speed X-ray imaging at 200 frames per second. This study showcases the structure design is significant for obtaining bright and fast perovskite scintillators for the real-time X-ray imaging.

Hybrid Eu(II)-bromide scintillators with efficient 5d-4f bandgap transition for X-ray imaging

Luminescent metal halides are attracting growing attention as scintillators for X-ray imaging in safety inspection, medical diagnosis, etc. Here we present brand-new hybrid Eu(II)-bromide scintillators, 1D type [Et4N]EuBr3·MeOH and 0D type [Me4N]6Eu5Br16·MeOH, with spin-allowed 5d-4f bandgap transition emission toward simplified carrier transport during scintillation process. The 1D/0D structures with edge/face -sharing [EuBr6]4- octahedra further contribute to lowing bandgaps and enhancing quantum confinement effect, enabling efficient scintillation performance (light yield ~73100 ± 800 Ph MeV-1, detect limit ~18.6 nGy s-1, X-ray afterglow ~ 1% @ 9.6 μs). We demonstrate the X-ray imaging with 27.3 lp mm-1 resolution by embedding Eu(II)-based scintillators into AAO film. Our results create the new family of low-dimensional rare-earth-based halides for scintillation and related optoelectronic applications.

Recent Advances in Fast-Decaying Metal Halide Perovskites Scintillators

Fast-decaying scintillators show subnanoseconds or nanoseconds lifetime and high time resolution, making them important in nuclear physics, medical diagnostics, scientific research, and other fields. Metal halide perovskites (MHPs) show great potential for scintillator applications owing to their easy synthesis procedure and attractive optical properties. However, MHPs scintillators still need further improvement in decay lifetime. To optimize the decay lifetime, great progress has been achieved recently. In this Perspective, we first summarize the structural characteristics of MHPs in various dimensions, which brings different exciton behaviors. Then, recent advances in designing fast-decaying MHPs according to different exciton behaviors have been concluded, focusing on the photophysical mechanisms to achieve fast-decaying lifetimes. These advancements in decay lifetimes could facilitate the MHPs scintillators in advanced applications, such as time-of-flight positron emission tomography (TOF-PET), photon-counting computed tomography (PCCT), etc. Finally, the challenges and future opportunities are discussed to provide a roadmap for designing novel fast-decaying MHPs scintillators.

Arising 2D Perovskites for Ionizing Radiation Detection

2D perovskites have greatly improved moisture stability owing to the large organic cations embedded in the inorganic octahedral structure, which also suppresses the ions migration and reduces the dark current. The suppression of ions migration by 2D perovskites effectively suppresses excessive device noise and baseline drift and shows excellent potential in the direct X-ray detection field. In addition, 2D perovskites have gradually emerged with many unique properties, such as anisotropy, tunable bandgap, high photoluminescence quantum yield, and wide range exciton binding energy, which continuously promote the development of 2D perovskites in ionizing radiation detection. This review aims to systematically summarize the advances and progress of 2D halide perovskite semiconductor and scintillator ionizing radiation detectors, including reported alpha (α) particle, beta (β) particle, neutron, X-ray, and gamma (γ) ray detection. The unique structural features of 2D perovskites and their advantages in X-ray detection are discussed. Development directions are also proposed to overcome the limitations of 2D halide perovskite radiation detectors.

Monolithic 2D Perovskites Enabled Artificial Photonic Synapses for Neuromorphic Vision Sensors

Neuromorphic visual sensors (NVS) based on photonic synapses hold a significant promise to emulate the human visual system. However, current photonic synapses rely on exquisite engineering of the complex heterogeneous interface to realize learning and memory functions, resulting in high fabrication cost, reduced reliability, high energy consumption and uncompact architecture, severely limiting the up-scaled manufacture, and on-chip integration. Here a photo-memory fundamental based on ion-exciton coupling is innovated to simplify synaptic structure and minimize energy consumption. Due to the intrinsic organic/inorganic interface within the crystal, the photodetector based on monolithic 2D perovskite exhibits a persistent photocurrent lasting about 90 s, enabling versatile synaptic functions. The electrical power consumption per synaptic event is estimated to be≈1.45 × 10-16 J, one order of magnitude lower than that in a natural biological system. Proof-of-concept image preprocessing using the neuromorphic vision sensors enabled by photonic synapse demonstrates 4 times enhancement of classification accuracy. Furthermore, getting rid of the artificial neural network, an expectation-based thresholding model is put forward to mimic the human visual system for facial recognition. This conceptual device unveils a new mechanism to simplify synaptic structure, promising the transformation of the NVS and fostering the emergence of next generation neural networks.

Overcoming Thermal Quenching in X-ray Scintillators through Multi-Excited State Switching

X-ray scintillators have gained significant attention in medical diagnostics and industrial applications. Despite their widespread utility, scintillator development faces a significant hurdle when exposed to elevated temperatures, as it usually results in reduced scintillation efficiency and diminished luminescence output. Here we report a molecular design strategy based on a hybrid perovskite (TpyBiCl5) that overcomes thermal quenching through multi-excited state switching. The structure of perovskite provides a platform to modulate the luminescence centers. The rigid framework constructed by this perovskite structure stabilized its triplet states, resulting in TpyBiCl5 exhibiting an approximately 12 times higher (45 % vs. 3.8 %) photoluminescence quantum yield of room temperature phosphorescence than that of its organic ligand (Tpy). Most importantly, the interactions between the components of this perovskite enable the mixing of different excited states, which has been revealed by experimental and theoretical investigations. The TpyBiCl5 scintillator exhibits a detection limit of 38.92 nGy s-1 at 213 K and a detection limit of 196.31 nGy s-1 at 353 K through scintillation mode switching between thermally activated delayed fluorescence and phosphorescence. This work opens up the possibility of solving the thermal quenching in X-ray scintillators by tuning different excited states.

Layered Chalcogenide Scintillators Enabled by Reversible Hydrous-Induced Phase Transformation for High-Resolution X-ray Imaging

Scintillation materials have been widely used in various fields, such as medical diagnosis and industrial detection. Chalcogenides have the potential to become a new generation of high-performance scintillation materials due to their high effective atomic number and good resistance to radiation damage. However, research on their application in radiation detection is currently very scarce. Herein, single crystals of rare earth ion-doped ternary chalcogenides NaGaS2/Eu were grown by a high-temperature solid-phase method. It exhibits unique characteristics of structure transformation by absorbing water molecules from the air. To maintain the anhydrous phase of the material, we have used a strategy of organic-inorganic composites of epoxy resin and NaGaS2/Eu to prepare devices for radiation detection and discuss the irradiation luminescence properties of the two phases. The anhydrous phase of NaGaS2/Eu demonstrates excellent sensitivity to X-rays, with a low detection limit of 250 nGy s-1, which is approximately 1/22 of the medical imaging dose. Additionally, composite flexible films were prepared, which exhibited excellent performance in X-ray imaging. These films enable clear observation of a wide range of objects with a high spatial resolution of up to 13.2 line pairs per millimeter (lp mm-1), indicating that chalcogenide holds promising prospects in the realm of X-ray imaging applications.

Stereo-Hindrance Engineering of A Cation toward <110>-Oriented 2D Perovskite with Minimized Tilting and High-Performance X-Ray Detection

2D <100>-oriented Dion-Jacobson or Ruddlesden-Popper perovskites are widely recognized as promising candidates for optoelectronic applications. However, the large interlayer spacing significantly hinders the carrier transport. <110>-oriented 2D perovskites naturally exhibit reduced interlayer spacings, but the tilting of metal halide octahedra is typically serious and leads to poor charge transport. Herein, a <110>-oriented 2D perovskite EPZPbBr4 (EPZ = 1-ethylpiperazine) with minimized tilting is designed through A-site stereo-hindrance engineering. The piperazine functional group enters the space enclosed by the three [PbBr6 ]4- octahedra, pushing Pb─Br─Pb closer to a straight line (maximum Pb─Br─Pb angle ≈180°), suppressing the tilting as well as electron-phonon coupling. Meanwhile, the ethyl group is located between layers and contributes an extremely reduced effective interlayer distance (2.22 Å), further facilitating the carrier transport. As a result, EPZPbBr4 simultaneously demonstrates high µτ product (1.8 × 10-3 cm2 V-1 ) and large resistivity (2.17 × 1010 Ω cm). The assembled X-ray detector achieves low dark current of 1.02 × 10-10 A cm-2 and high sensitivity of 1240 µC Gy-1 cm-2 under the same bias voltage. The realized specific detectivity (ratio of sensitivity to noise current density, 1.23 × 108 µC Gy-1 cm-1 A-1/2 ) is the highest among all reported perovskite X-ray detectors.

Light Management of Metal Halide Scintillators for High-Resolution X-Ray Imaging

The ever-growing need to inspect matter with hyperfine structures requires a revolution in current scintillation detectors, and the innovation of scintillators is revived with luminescent metal halides entering the scene. Notably, for any scintillator, two fundamental issues arise: Which kind of material is suitable and in what form should the material exist? The answer to the former question involves the sequence of certain atoms into specific crystal structures that facilitate the conversion of X-ray into light, whereas the answer to the latter involves assembling these crystallites into particular material forms that can guide light propagation toward its corresponding pixel detector. Despite their equal importance, efforts are overwhelmingly devoted to improving the X-ray-to-light conversion, while the material-form-associated light propagation, which determines the optical signal collected for X-ray imaging, is largely overlooked. This perspective critically correlates the reported spatial resolution with the light-propagation behavior in each form of metal halides, combing the designing rules for their future development.