Halide lead perovskites for ionizing radiation detection

Enabling low-drift flexible perovskite photodetectors by electrical modulation for wearable health monitoring and weak light imaging

Metal halide perovskites are promising for next-generation flexible photodetectors owing to their low-temperature solution processability, mechanical flexibility, and excellent photoelectric properties. However, the defects and notorious ion migration in polycrystalline metal halide perovskites often lead to high and unstable dark current, thus deteriorating their detection limit and long-term operations. Here, we propose an electrical field modulation strategy to significantly reduce the dark current of metal halide perovskites-based flexible photodetector more than 1000 times (from ~5 nA to ~5 pA). Meanwhile, ion migration in metal halide perovskites is effectively suppressed, and the metal halide perovskites-based flexible photodetector shows a long-term continuous operational stability (~8000 s) with low signal drift (~4.2 × 10-4 pA per second) and ultralow dark current drift (~1.3 × 10-5 pA per second). Benefitting from the electrical modulation strategy, a high signal-to-noise ratio wearable photoplethysmography sensor and an active-matrix photodetector array for weak light imaging are successfully demonstrated. This work offers a universal strategy to improve the performance of metal halide perovskites for wearable flexible photodetector and image sensor applications.

Multicomponent X-ray Shielding Using Sulfated Cerium Oxide and Bismuth Halide Composites

Lead is the most widely used X-ray-shielding material, but it is heavy (density ≈ 11.34 g/cm3) and toxic. Therefore, the replacement of Pb with lightweight, ecofriendly materials would be beneficial, and such materials would have applications in medicine, electronics, and aerospace engineering. However, the shielding ability of Pb-free materials is significantly lower than that of Pb itself. To maximize the radiation attenuation of non-Pb-based shielding materials, a high-attenuation cross-section, normal to the incoming X-ray direction, must be achieved. In this study, we developed efficient X-ray-shielding materials composed of sulfated cerium oxide (S-CeO2) and bismuth halides. Crucially, the materials are lightweight and mechanically flexible because of the absence of heavy metals (for example, Pb and W). Further, by pre-forming the doped metal oxide as a porous sponge matrix, and then incorporating the bismuth halides into the porous matrix, uniform, compact, and intimate composites with a high-attenuation cross-section were achieved. Owing to the synergetic effect of the doped metal oxide and bismuth halides, the resultant thin (approximately 3 mm) and lightweight (0.85 g·cm-3) composite achieved an excellent X-ray-shielding rate of approximately 92% at 60 kV, one of the highest values reported for non-heavy-metal shielding materials.

Synergy of 3D and 2D Perovskites for Durable, Efficient Solar Cells and Beyond

Three-dimensional (3D) organic-inorganic lead halide perovskites have emerged in the past few years as a promising material for low-cost, high-efficiency optoelectronic devices. Spurred by this recent interest, several subclasses of halide perovskites such as two-dimensional (2D) halide perovskites have begun to play a significant role in advancing the fundamental understanding of the structural, chemical, and physical properties of halide perovskites, which are technologically relevant. While the chemistry of these 2D materials is similar to that of the 3D halide perovskites, their layered structure with a hybrid organic-inorganic interface induces new emergent properties that can significantly or sometimes subtly be important. Synergistic properties can be realized in systems that combine different materials exhibiting different dimensionalities by exploiting their intrinsic compatibility. In many cases, the weaknesses of each material can be alleviated in heteroarchitectures. For example, 3D-2D halide perovskites can demonstrate novel behavior that neither material would be capable of separately. This review describes how the structural differences between 3D halide perovskites and 2D halide perovskites give rise to their disparate materials properties, discusses strategies for realizing mixed-dimensional systems of various architectures through solution-processing techniques, and presents a comprehensive outlook for the use of 3D-2D systems in solar cells. Finally, we investigate applications of 3D-2D systems beyond photovoltaics and offer our perspective on mixed-dimensional perovskite systems as semiconductor materials with unrivaled tunability, efficiency, and technologically relevant durability.

Lead-Free Halide Perovskites for Direct X-Ray Detectors

Lead halide perovskites have made remarkable progress in the field of radiation detection owing to the excellent and unique optoelectronic properties. However, the instability and the toxicity of lead-based perovskites have greatly hindered its practical applications. Alternatively, lead-free perovskites with high stability and environmental friendliness thus have fascinated significant research attention for direct X-ray detection. In this review, the current research progress of X-ray detectors based on lead-free halide perovskites is focused. First, the synthesis methods of lead-free perovskites including single crystals and films are discussed. In addition, the properties of these materials and the detectors, which can provide a better understanding and designing satisfactory devices are also presented. Finally, the challenge and outlook for developing high-performance lead-free perovskite X-ray detectors are also provided.

Centimeter-Sized Single Crystals of Dion-Jacobson Phase Lead-Free Double Perovskite for Efficient X-ray Detection

2D Dion-Jacobson (DJ) phase hybrid perovskites have shown great promise in the photoelectronic field owing to their outstanding optoelectronic performance and superior structural rigidity. However, DJ phase lead-free double perovskites are still a virgin land with direct X-ray detection. Herein, we have designed and synthesized a new DJ phase lead-free layered double perovskite of (HIS)2 AgSbBr8 (1, HIS2+  = histammonium). Centimeter-sized (18 × 10 × 5 mm3 ) single crystals of 1 are successfully grown via the temperature cooling technique, exhibiting remarkable semiconductive characteristics such as a high resistivity (2.2 × 1011  Ω cm), a low trap state density (3.56 × 1010 cm-3 ), and a large mobility-lifetime product (1.72 × 10-3 cm2 V-1 ). Strikingly, its single-crystal-based X-ray detector shows a high sensitivity of 223 µC Gy-1 air cm-2 under 33.3 V mm-1 , a low detection limit (84.2 nGyair s-1 ) and superior anti-fatigue. As far as we know, we firstly demonstrates the potential of 2D DJ phase lead-free hybrid double perovskite in X-ray detection, showing excellent photoelectric response and operational stability. This work will pave a promising pathway to the innovative application of hybrid perovskites for eco-friendly and efficient X-ray detection.

Solution-Grown MAPbBr3 Single Crystals for Self-Powered Detection of X-rays with High Energies above One Megaelectron Volt

Perovskite single crystals are actively studied as X-ray detection materials with enhanced sensitivity. Moreover, the feasibility of using perovskites for self-powered devices such as photodetectors, UV detectors, and X-ray detectors can significantly expand their application range. In this work, the charge carrier transport and photocurrent properties of MAPbBr3 single crystals (MSCs) are improved by the mechanochemical surface treatment using glycerin combined with an additional electrode design that forms an ohmic contact. The sensitivity of MSC-based detectors and pulse shape generated by X-rays are enhanced at various bias voltages. The synthesized MSC detectors generate direction-dependent photocurrents, which indicate the presence of a polarization-induced internal electric field. In addition, photocurrent signals are produced by X-rays with energies greater than 1 MeV under a zero-bias voltage. This work demonstrates a high application potential of perovskites as self-powered detectors for X-rays with energies exceeding 1 MeV.

Advances in the Application of Perovskite Materials

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

Perovskite-Based X-ray Detectors

X-ray detection has widespread applications in medical diagnosis, non-destructive industrial radiography and safety inspection, and especially, medical diagnosis realized by medical X-ray detectors is presenting an increasing demand. Perovskite materials are excellent candidates for high-energy radiation detection based on their promising material properties such as excellent carrier transport capability and high effective atomic number. In this review paper, we introduce X-ray detectors using all kinds of halide perovskite materials along with various crystal structures and discuss their device performance in detail. Single-crystal perovskite was first fabricated as an active material for X-ray detectors, having excellent performance under X-ray illumination due to its superior photoelectric properties of X-ray attenuation with μm thickness. The X-ray detector based on inorganic perovskite shows good environmental stability and high X-ray sensitivity. Owing to anisotropic carrier transport capability, two-dimensional layered perovskites with a preferred orientation parallel to the substrate can effectively suppress the dark current of the device despite poor light response to X-rays, resulting in lower sensitivity for the device. Double perovskite applied for X-ray detectors shows better attenuation of X-rays due to the introduction of high-atomic-numbered elements. Additionally, its stable crystal structure can effectively lower the dark current of X-ray detectors. Environmentally friendly lead-free perovskite exhibits potential application in X-ray detectors by virtue of its high attenuation of X-rays. In the last section, we specifically introduce the up-scaling process technology for fabricating large-area and thick perovskite films for X-ray detectors, which is critical for the commercialization and mass production of perovskite-based X-ray detectors.

Correlative Imaging of Individual CsPbBr3 Nanocrystals: Role of Isolated Grains in Photoluminescence of Perovskite Polycrystalline Thin Films

We report on the optical properties of a CsPbBr₃ polycrystalline thin film on a single grain level. A sample composed of isolated nanocrystals (NCs) mimicking the properties of the polycrystalline thin film grains that can be individually probed by photoluminescence spectroscopy was prepared. These NCs were analyzed using correlative microscopy allowing the examination of structural, chemical, and optical properties from identical sites. Our results show that the stoichiometry of the CsPbBr₃ NCs is uniform and independent of the NCs' morphology. The photoluminescence (PL) peak emission wavelength is slightly dependent on the dimensions of NCs, with a blue shift up to 9 nm for the smallest analyzed NCs. The magnitude of the blueshift is smaller than the emission line width, thus detectable only by high-resolution PL mapping. By comparing the emission energies obtained from the experiment and a rigorous effective mass model, we can fully attribute the observed variations to the size-dependent quantum confinement effect.

Efficient X-ray luminescence imaging with ultrastable and eco-friendly copper(I)-iodide cluster microcubes

The advancement of contemporary X-ray imaging heavily depends on discovering scintillators that possess high sensitivity, robust stability, low toxicity, and a uniform size distribution. Despite significant progress in this field, the discovery of a material that satisfies all of these criteria remains a challenge. In this study, we report the synthesis of monodisperse copper(I)-iodide cluster microcubes as a new class of X-ray scintillators. The as-prepared microcubes exhibit remarkable sensitivity to X-rays and exceptional stability under moisture and X-ray exposure. The uniform size distribution and high scintillation performance of the copper(I)-iodide cluster microcubes make them suitable for the fabrication of large-area, flexible scintillating films for X-ray imaging applications in both static and dynamic settings.

Radioluminescent Cu-Au Metal Nanoclusters: Synthesis and Self-Assembly for Efficient X-ray Scintillation and Imaging

Zero-dimensional (0D) scintillation materials have drawn tremendous attention due to their inherent advantages in the fabrication of flexible high-energy radiation scintillation screens by solution processes. Although considerable progress has been made in the development of 0D scintillators, such as the current leading lead-halide perovskite nanocrystals and quantum dots, challenges still persist, including potential issues with self-absorption, air stability, and eco-friendliness. Here, we present a strategy to overcome those limitations by synthesis and self-assembly of a new class of scintillators based on metal nanoclusters. We demonstrate the gram-scale synthesis of an atomically precise nanocluster with a Cu-Au alloy core exhibiting high phosphorescence quantum yield, aggregation-induced emission enhancement (AIEE) behavior, and intense radioluminescence. By controlling solvent interactions, the AIEE-active nanoclusters were self-assembled into submicron spherical superparticles in solution, which we exploited as a novel building block for flexible particle-deposited scintillation films with high-resolution X-ray imaging performance. This work reveals metal nanoclusters and their self-assembled superstructures as a promising class of scintillators for practical applications in high-energy radiation detection and imaging.

Composition Engineering Growth of Cs3Bi2I9 Single Crystals with Low Defect Density for X-ray Detectors

Cs₃Bi₂I₉ (CBI) single crystal (SC) is a promising material for a higher-performance direct X-ray detector. However, the composition of CBI SC prepared by the solution method usually deviates from the ideal stoichiometric ratio, which limits the detector performance. In this paper, based on the finite element analysis method, the growth model of the top-seed solution method has been established, and then the influence of precursor ratio, temperature field, and other parameters on the composition of CBI SC has been simulated. The simulation results were used to guide the growth of the CBI SCs. Finally, a high-quality CBI SC with a stoichiometric ratio of Cs/Bi/I = 2.87:2:8.95 has been successfully grown, and the defect density is as low as 1.03 × 10⁹ cm^-3, the carrier lifetime is as high as 16.7 ns, and the resistivity is as high as 1.44 × 10¹² Ω·cm. The X-ray detector based on this SC has a sensitivity of 29386.2 μC·Gy_air^-1 cm^-2 at an electric field of 40 V·mm^-1, and a low detection limit of 0.36 nGy_air·s^-1, creating a record for the all-inorganic perovskite materials.

Solution-Processed Hybrid Europium (II) Iodide Scintillator for Sensitive X-Ray Detection

Lead halide perovskite nanocrystals have recently demonstrated great potential as x-ray scintillators, yet they still suffer toxicity issues, inferior light yield (LY) caused by severe self-absorption. Nontoxic bivalent europium ions (Eu2+) with intrinsically efficient and self-absorption-free d-f transition are a prospective replacement for the toxic Pb2+. Here, we demonstrated solution-processed organic-inorganic hybrid halide BA10EuI12 (BA denotes C4H9NH4+) single crystals for the first time. BA10EuI12 was crystallized in a monoclinic space group of P21/c, with photoactive sites of [EuI6]4- octahedra isolated by BA+ cations, which exhibited high photoluminescence quantum yield of 72.5% and large Stokes shift of 97 nm. These properties enable an appreciable LY value of 79.6% of LYSO (equivalent to ~27,000 photons per MeV) for BA10EuI12. Moreover, BA10EuI12 shows a short excited-state lifetime (151 ns) due to the parity-allowed d-f transition, which boosts the potential of BA10EuI12 for use in real-time dynamic imaging and computer tomography applications. In addition, BA10EuI12 demonstrates a decent linear scintillation response ranging from 9.21 μGyair s-1 to 145 μGyair s-1 and a detection limit as low as 5.83 nGyair s-1. The x-ray imaging measurement was performed using BA10EuI12 polystyrene (PS) composite film as a scintillation screen, which exhibited clear images of objects under x-ray irradiation. The spatial resolution was determined to be 8.95 lp mm-1 at modulation transfer function = 0.2 for BA10EuI12/PS composite scintillation screen. We anticipate that this work will stimulate the exploration of d-f transition lanthanide metal halides for sensitive x-ray scintillators.

Interlayer-Spacing Engineering of Lead-Free Perovskite Single Crystal for High-Performance X-Ray Imaging

Lead-free A₃ Bi₂ I₉ -type perovskites are demonstrated as a class of promising semiconductors for high-performance X-ray detection due to their high bulk resistivity and strong X-ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c-axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A-site cation of aminoguanidinium (AG) with all-NH₂ terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG₃ Bi₂ I₉ single crystals (SCs) render shorter interlamellar distance for a larger mobility-lifetime product of 7.94 × 10^-3  cm²  V^-1 , which is three times higher than the value measured on the best MA₃ Bi₂ I₉ SC (2.87 × 10^-3  cm²  V^-1 ). Therefore, the X-ray detectors fabricated on the AG₃ Bi₂ I₉ SC exhibit high sensitivity of 5791 uC Gy^-1  cm^-2 , a low detection limit of 2.6 nGy s^-1, and a short response time of 690 µs, all of which are far better than those of the state-of-the-art MA₃ Bi₂ I₉ SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lp mm^-1 ) X-ray imaging. This work will facilitate the development of low-cost and high-performance lead-free X-ray detectors.

Printable Perovskite Diodes for Broad-Spectrum Multienergy X-Ray Detection

Multienergy X-ray detection is critical to effectively differentiate materials in a variety of diagnostic radiology and nondestructive testing applications. Silicon and selenium X-ray detectors are the most common for multienergy detection; however, these present poor energy discrimination across the broad X-ray spectrum and exhibit limited spatial resolution due to the high thicknesses required for radiation attenuation. Here, an X-ray detector based on solution-processed thin-film metal halide perovskite that overcomes these challenges is introduced. By harnessing an optimized n-i-p diode configuration, operation is achieved across a broad range of soft and hard X-ray energies stemming from 0.1 to 10's of keV. Through detailed experimental and simulation work, it is shown that optimized Cs_0.1 FA_0.9 PbI₃ perovskites effectively attenuate soft and hard X-rays, while also possessing excellent electrical properties to result in X-ray detectors with high sensitivity factors that exceed 5 × 10³ µ C   G y Vac - 1   cm - 2 $\mu {\rm{C}}\;{{\bf Gy}}_{{\rm{Vac}}}^{ - 1}\;{\rm{c}}{{\rm{m}}^{ - 2}}$ and 6 × 10⁴ µC Gy^-1 cm^-2 within soft and hard X-ray regimes, respectively. Harnessing the solution-processable nature of the perovskites, roll-to-roll printable X-ray detectors on flexible substrates are also demonstrated.

Prominent Free Charges Tunneling Through Organic Interlayer of 2D Perovskites

The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4-(2-Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)₂ PbI₄ and DJ (4AEPy)PbI₄ from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH₃ , respectively. The interaction of N-H···N hydrogen bond between adjacent organic molecules in (4AEPy)₂ PbI₄ leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)₂ PbI₄ ) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI₄ are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI₄ device displays better light response and X-ray detection capability with a high sensitivity of 5627 µC Gy_air ^-1 cm^-2 and the lowest detectable dose rate of 20 nGy_air s^-1 .

Laser Scribing for Electrode Patterning of Perovskite Spectrometer-Grade CsPbBr3 Gamma-ray Detectors

Making semiconductor radiation detectors that work at room temperature relies heavily on the deposition and pixelation of electrodes. Electrode patterning of perovskite solar cells widely implements laser scribing techniques, which is a convenient, scalable, and inexpensive technique. However, this method has not found its application in radiation detector patterning yet, and the question whether laser scribing can achieve high-quality patterns with minimum damage to a detector crystal and low interpixel cross-talk remains largely unanswered. To prove that laser scribing is a practical method for electrode patterning on perovskite CsPbBr₃ detectors, we use the material to create a variety of patterns. A very low lateral leakage current (60 nA at 10 V) and high mobility-lifetime product (9.7(3) × 10^-4 cm²/V) were observed between the pixel and the guard ring in tests of single-pixel devices with a separation of 200 or 100 μm between the central electrode and the guard ring. The 122 and 136 keV photopeaks in ⁵⁷Co gamma-ray spectra were very well resolved with an energy resolution of up to 6.1% at 122 keV. A further reduction in gap size to 50 μm is conceivable, but more process optimization is needed.

Detector-grade perovskite single-crystal wafers via stress-free gel-confined solution growth targeting high-resolution ionizing radiation detection

Solution-processed organic‒inorganic halide perovskite (OIHP) single crystals (SCs) have demonstrated great potential in ionizing radiation detection due to their outstanding charge transport properties and low-cost preparation. However, the energy resolution (ER) and stability of OIHP detectors still lag far behind those of melt-grown inorganic perovskite and commercial CdZnTe counterparts due to the absence of detector-grade high-quality OIHP SCs. Here, we reveal that the crystallinity and uniformity of OIHP SCs are drastically improved by relieving interfacial stress with a facial gel-confined solution growth strategy, thus enabling the direct preparation of large-area detector-grade SC wafers up to 4 cm with drastically suppressed electronic and ionic defects. The resultant radiation detectors show both a small dark current below 1 nA and excellent baseline stability of 4.0 × 10^-8nA cm^-1 s^-1 V^-1, which are rarely realized in OIHP detectors. Consequently, a record high ER of 4.9% at 59.5 keV is achieved under a standard ²⁴¹Am gamma-ray source with an ultralow operating bias of 5 V, representing the best gamma-ray spectroscopy performance among all solution-processed semiconductor radiation detectors ever reported.

Ultrahigh-Flux X-ray Detection by a Solution-Grown Perovskite CsPbBr3 Single-Crystal Semiconductor Detector

Solution-processed perovskites are promising for hard X-ray and gamma-ray detection, but there are limited reports on their performance under extremely intense X-rays. Here, a solution-grown all-inorganic perovskite CsPbBr₃ single-crystal semiconductor detector capable of operating at ultrahigh X-ray flux of 10¹⁰ photons s^-1 mm^-2 is reported. High-quality solution-grown CsPbBr₃ single crystals are fabricated into detectors with a Schottky diode structure of eutectic gallium indium/CsPbBr₃ /Au. A high reverse-bias voltage of 1000 V (435 V mm^{- 1} ) can be applied with a small and stable dark current of ≈60-70 nA (≈9-10 nA mm^{- 2} ), which enables a high sensitivity larger than 10 000 µC Gy_air ^-1 cm^{- 2} and a simultaneous low detection limit of 22 nGy_air s^{- 1} . The CsPbBr₃ semiconductor detector shows an excellent photocurrent linearity and reproducibility under 58.61 keV synchrotron X-rays with flux from 10⁶ to 10¹⁰ photons s^{- 1} mm^{- 2} . Defect characterization by thermally stimulated current spectroscopy shows a similar low defect density of a synchrotron X-ray and a lab X-ray irradiated device. Solid-state nuclear magnetic resonance spectroscopy suggests that the excellent performance of the solution-grown CsPbBr₃ single crystal may be associated with its good short-range order, comparable to the spectrometer-grade melt-grown CsPbBr₃ .

Porous and Water Stable 2D Hybrid Metal Halide with Broad Light Emission and Selective H2 O Vapor Sorption

In this work we report a strategy for generating porosity in hybrid metal halide materials using molecular cages that serve as both structure-directing agents and counter-cations. Reaction of the [2.2.2] cryptand (DHS) linker with Pb^II in acidic media gave rise to the first porous and water-stable 2D metal halide semiconductor (DHS)₂ Pb₅ Br₁₄ . The corresponding material is stable in water for a year, while gas and vapor-sorption studies revealed that it can selectively and reversibly adsorb H₂ O and D₂ O at room temperature (RT). Solid-state NMR measurements and DFT calculations verified the incorporation of H₂ O and D₂ O in the organic linker cavities and shed light on their molecular configuration. In addition to porosity, the material exhibits broad light emission centered at 617 nm with a full width at half-maximum (FWHM) of 284 nm (0.96 eV). The recorded water stability is unparalleled for hybrid metal halide and perovskite materials, while the generation of porosity opens new pathways towards unexplored applications (e.g. solid-state batteries) for this class of hybrid semiconductors.

Design and Simulated Electrical Properties of a Proposed Implanted-Epi Silicon 3D-Spherical Electrode Detector

A new type of 3D electrode detector, named here as the Implanted-Epi Silicon 3D-Spherical Electrode Detector, is proposed in this work. Epitaxial and ion implantation processes can be used in this new detector, allowing bowl-shaped electrodes to penetrate the silicon completely. The distance between the bowl cathode and the central collection electrode is basically the same, thus the total depletion voltage of Implanted-Epi Silicon 3D-Spherical Electrode Detectors is no longer directively correlated with the thickness of the silicon wafer, but only related to the electrode spacing. In this work, we model the device physics of this new structure and use a simulation program to conduct a systematic 3D simulation of its electrical characteristics, including electric potential and electric field distributions, electron concentration profile, leakage current, and capacitance, and compare it to the traditional 3D detectors. The theoretical and simulation study found that the internal electric potential of the new detector was smooth and no potential saddle point was found. The electric field is also uniform, and there is no zero field and a low electric field area. Compared with the traditional silicon 3D electrode detectors, the full depletion voltage is greatly reduced and the charge collection efficiency is improved. As a large electrode spacing (up to 500 μm) can be realized in the Implanted-Epi Silicon 3D-Spherical Electrode Detector thanks to their advantage of a greatly reduced full depletion voltage, detectors with large pixel cells (and thus small dead volume) can be developed for applications in photon science (X-ray, among others).

Realizing nearly-zero dark current and ultrahigh signal-to-noise ratio perovskite X-ray detector and image array by dark-current-shunting strategy

Although perovskite X-ray detectors have revealed promising properties, their dark currents are usually hundreds of times larger than the practical requirements. Here, we report a detector architecture with a unique shunting electrode working as a blanking unit to suppress dark current, and it theoretically can be reduced to zero. We experimentally fabricate the dark-current-shunting X-ray detector, which exhibits a record-low dark current of 51.1 fA at 5 V mm^-1, a detection limit of 7.84 nGy_air s^-1, and a sensitivity of 1.3 × 10⁴ μC Gy_air^-1 cm^-2. The signal-to-noise ratio of our polycrystalline perovskite-based detector is even outperforming many previously reported state-of-the-art single crystal-based X-ray detectors by serval orders of magnitude. Finally, the proof-of-concept X-ray imaging of a 64 × 64 pixels dark-current-shunting detector array is successfully demonstrated. This work provides a device strategy to fundamentally reduce dark current and enhance the signal-to-noise ratio of X-ray detectors and photodetectors in general.

Recent Development of Halide Perovskite Materials and Devices for Ionizing Radiation Detection

Ionizing radiation such as X-rays and γ-rays has been extensively studied and used in various fields such as medical imaging, radiographic nondestructive testing, nuclear defense, homeland security, and scientific research. Therefore, the detection of such high-energy radiation with high-sensitivity and low-cost-based materials and devices is highly important and desirable. Halide perovskites have emerged as promising candidates for radiation detection due to the large light absorption coefficient, large resistivity, low leakage current, high mobility, and simplicity in synthesis and processing as compared with commercial silicon (Si) and amorphous selenium (a-Se). In this review, we provide an extensive overview of current progress in terms of materials development and corresponding device architectures for radiation detection. We discuss the properties of a plethora of reported compounds involving organic-inorganic hybrid, all-inorganic, all-organic perovskite and antiperovskite structures, as well as the continuous breakthroughs in device architectures, performance, and environmental stability. We focus on the critical advancements of the field in the past few years and we provide valuable insight for the development of next-generation materials and devices for radiation detection and imaging applications.

Lattice-Distortion-Induced Change in the Magnetic Properties in Br-Defect Host CsPbBr3 Perovskite Quantum Dots

Herein, we report temperature- and field-induced magnetic states in CsPbBr₃ perovskite quantum dots (PQDs) attributed to Br defects. We find that temperature-dependent structural distortion is the main source of various temperature-induced magnetic states in Br-defect host CsPbBr₃ PQDs. Comprehensively examined magnetization data through Arrott plots, Langevin and Brillouin function fitting, and structural analysis reveal the presence of various oxidation states (i.e., Pb⁰, Pb⁺, Pb²⁺, and Pb³⁺) yielding different magnetic states, such as diamagnetic states above 90 K, paramagnetic states below ≈90 K, and perhaps locally ordered states between 58 and 90 K. It is realized from theoretical fits that paramagnetic ions exist (i.e., superparamagnetic behavior) due to Br defects causing Pb⁺ (and/or Pb³⁺ ions) in the diamagnetic region. We anticipate that our findings will spur future research of the development of spin-optoelectronics, such as spin light-emitting diodes, and spintronics devices based on CsPbBr₃ PQDs.

Simple Visualization of Universal Ferroelastic Domain Walls in Lead Halide Perovskites

Domain features and domain walls in lead halide perovskites (LHPs) have attracted broad interest due to their potential impact on optoelectronic properties of this unique class of solution-processable semiconductors. Using nonpolarized light and simple imaging configurations, ferroelastic twin domains and their switchings through multiple consecutive phase transitions are directly visualized. This direct optical contrast originates from finite optical reflections at the wall interface between two compositionally identical, orientationally different, optically anisotropic domains inside the material bulk. The findings show these domain walls serve as internal reflectors and steer energy transport inside halide perovskites optically. First-principles calculations show universal low domain-wall energies and modest energy barriers of domain switching, confirming their prevalent appearance, stable presence, and facile moving observed in the experiments. The generality of ferroelasticity in halide perovskites stems from their soft bonding characteristics. This work shows the feasibility of using LHP twin domain walls as optical guides of internal photoexcitations, capable of nonvolatile on-off switching and tunable positioning endowed by their universal ferroelasticity.

Growth and Self-Assembly of CsPbBr3 Nanocrystals in the TOPO/PbBr2 Synthesis as Seen with X-ray Scattering

Despite broad interest in colloidal lead halide perovskite nanocrystals (LHP NCs), their intrinsic fast growth has prevented controlled synthesis of small, monodisperse crystals and insights into the reaction mechanism. Recently, a much slower synthesis of LHP NCs with extreme size control has been reported, based on diluted TOPO/PbBr₂ precursors and a diisooctylphosphinate capping ligand. We report new insights into the nucleation, growth, and self-assembly in this reaction, obtained by in situ synchrotron-based small-angle X-ray scattering and optical absorption spectroscopy. We show that dispersed 3 nm Cs[PbBr₃] agglomerates are the key intermediate species: first, they slowly nucleate into crystals, and then they release Cs[PbBr₃] monomers for further growth of the crystals. We show the merits of a low Cs[PbBr₃] monomer concentration for the reaction based on oleate ligands. We also examine the spontaneous superlattice formation mechanism occurring when the growing nanocrystals in the solvent reach a critical size of 11.6 nm.

Highly Efficient, Flexible, and Eco-Friendly Manganese(II) Halide Nanocrystal Membrane with Low Light Scattering for High-Resolution X-ray Imaging

Scintillators enable invisible X-ray to be converted into ultraviolet (UV)/visible light that can be collected using a sensor array and is the core component of the X-ray imaging system. However, combining the excellent properties of high light output, high spatial resolution, flexibility, non-toxicity, and cost effectiveness into a single X-ray scintillator remains a great challenge. Herein, a novel scintillator based on benzyltriphenylphosphonium manganese(II) bromide (BTP₂MnBr₄) nanocrystal (NC) membranes was developed by the in situ fabrication strategy. The long Mn-Mn distance provided by the large BTP cation allows the nonradiative energy dissipation in this manganese(II) halide to be significantly suppressed. As a result, the flexible BTP₂MnBr₄ NC scintillator shows an excellent linear response to the X-ray dose rate, a high light yield of ∼71,000 photon/MeV, a low detection limit of 86.2 nGy_air/s at a signal-to-noise ratio of 3, a strong radiation hardness, and a long-term thermal stability. Thanks to the low Rayleigh scattering associated with the dense distribution of nanometer-scale emitters, light cross-talk in X-ray imaging is greatly suppressed. The impressively high-spatial resolution X-ray imaging (23.8 lp/mm at modulation transfer function = 0.2 and >20 lp/mm for a standard pattern chart) was achieved on this scintillator. Moreover, well-resolved 3D dynamic rendering X-ray projections were also successfully demonstrated using this scintillator. These results shed light on designing efficient, flexible, and eco-friendly scintillators for high-resolution X-ray imaging.

Perovskite-like Silver Halide Single-Crystal Microbelt Enables Ultrasensitive Flexible X-ray Detectors

Lead halide perovskite single crystals have attracted wide interest in the field of X-ray detection due to their excellent photophysical properties. However, their inherent toxicity and high thickness restrict their applications in flexible devices. In this paper, designing a micronanometer-scale X-ray detector based on all-inorganic lead-free CsAg2I3 (CAI) single crystal microbelts (MBs) has addressed the above issues. These CAI single crystal MBs can be synthesized on various substrates with high crystal quality and excellent stability. Based on their excellent characteristics of the CAI MBs, we fabricate single CAI MB devices with an Au/CAI/Au structure, which shows not only good ultraviolet photoresponse characteristics, but also excellent X-ray detection performance. The optimized CAI photodetectors exhibit a responsivity of 23.59 mA/W, a high detectivity of 1010 Jones, and a fast response speed. For X-ray detection performance, a sensitivity of up to 515.49 μC Gyair-1 cm-2 and a detection limit of as low as 14.65 μGyair s-1 are achieved with outstanding operation stability and excellent long-term stability. Furthermore, our devices also showed excellent applicability for X-ray imaging, which is promising for their use in X-ray detection and imaging. Finally, flexible X-ray detectors are fabricated by using thin CAI single-crystal MBs and demonstrate good flexibility under different bending radii and bending cycles. Our work shows the potential for developing highly sensitive flexible integrated micro/nano optoelectronic devices by using lead-free perovskite analogue single crystals.

Metal-halide perovskites for high-efficiency radiation shielding applications

The ionizing radiation possesses extremely strong penetration capability, which poses serious risk on the health of the human body and jeopardize electronics. Here the authors demonstrate that MAPbI₃/epoxy composites prepared by a simple method show high radiation shielding performance.

Development of a real-time in vivo dosimetry tool for electron beam therapy using a flexible thin film solar cell coated with scintillator powder

PURPOSE

A real-time solar cell based in vivo dosimetry system (SC-IVD) was developed using a flexible thin film solar cell and scintillating powder. The present study evaluated the clinical feasibility of the SC-IVD in electron beam therapy.

METHODS

A thin film solar cell was coated with 100 mg of scintillating powder using an optical adhesive to enhance the sensitivity of the SC-IVD. Calibration factors were obtained by dividing the dose, measured at a reference depth for 6-20 MeV electron beam energy, by the signal obtained using the SC-IVD. Dosimetric characteristics of SC-IVDs containing variable quantities of scintillating powder (0-500 mg) were evaluated, including energy, dose rate, and beam angle dependencies, as well as dose linearity. To determine the extent to which the SC-IVD affected the dose to the medium, doses at R90 were compared depending on whether the SC-IVD was on the surface. Finally, the accuracy of surface doses measured using the SC-IVD was evaluated by comparison with surface doses measured using a Markus chamber.

RESULTS

Charge measured using the SC-IVD increased linearly with dose and was within 1% of the average signal according to the dose rate. The signal generated by the SC-IVD increased as the beam angle increased. The presence of the SC-IVD on the surface of a phantom resulted in a 0.5%-2.2% reduction in dose at R90 for 6-20 MeV electron beams compared with the bare phantom. Surface doses measured using the SC-IVD system and Markus chamber differed by less than 5%.

CONCLUSIONS

The dosimetric characteristics of the SC-IVD were evaluated in this study. The results showed that it accurately measured the surface dose without a significant difference of dose in the medium when compared with the Markus chamber. The flexibility of the SC-IVD allows it to be attached to a patient's skin, enabling real-time and cost-effective measurement.

Diffuse Reflectance Spectroscopy with Dilution: A Powerful Method for Halide Perovskites Study

Halide perovskites and their low-dimensional analogs are promising semiconductor materials for solar cells, LEDs, lasers, detectors and other applications in the area of photonics. The most informative optical property of semiconductor photonics materials is the absorption spectrum enabling observation of the fundamental absorption edge, exciton structure, defect-related bands, etc. Traditionally, in the study of halide perovskites, this spectrum is obtained by absorption spectroscopy of thin films or diffuse reflectance spectroscopy of powders. The first method is applicable only to compounds with the developed thin film deposition technology, and in the second case, a large absorption coefficient narrows the observations down to the sample transparency region. In this paper, we suggest the diffuse reflectance spectroscopy with dilution as a method for obtaining the full-range absorption spectrum from halide perovskite powders, and demonstrate its application to practically important cases.

Crystal and Electronic Structures of New Two Dimensional 3-NH3-PyPbX4 Haloplumbate Materials

In this study, we explored both the crystal and electronic structures of new synthesized materials 3-NH₃-PyPbX₄ (X = Br, I). Both compounds are isostructural, and they crystallize in the monoclinic space group P2₁/c, with four formula units in the unit cell. According to the analysis of their electronic structures, both compounds are direct semiconductors with direct transitions between valence and conduction bands occurring at the k-points A, Z, and at about half of the distance between the k-points D/D1 and D1/E. An inspection of DOS reveals that, in both perovskites, the highest energy VBs are comprised mainly of electronic states of halogen anions, while the lowest states in the conduction band originate from lead orbitals. In addition, there are two flat bands composed of electronic states of carbon and nitrogen originating from the organic subsystems and presumably corresponding to the π* orbitals of 3-NH₃-C₅H₆N cations. Both materials demonstrate a broad luminescence emission. Two mechanisms of the radiative relaxation based on either self-trapped excitons or on charge transfers between inorganic and organic subsystems are discussed.

Excitonic Enhancement and Excited Excitonic States in CsPbBr3 Halide Perovskite Single Crystals

Halide perovskites are novel photonics materials promising numerous applications in fields such as photovoltaics, LED light sources, microlasers, and radiation detectors. Many halide perovskites are direct-gap semiconductors, and Wannier-Mott excitons play a significant role in their optical properties near the fundamental absorption edge. The high oscillator strength of these states favors applications where efficient interaction with light is required. In this work, to study excitonic states in CsPbBr3 halide perovskite single crystals, the reflection spectroscopy at temperatures from 4 K was used. A reflection coefficient up to 70% was observed for the n=1 exciton state, followed by weak excited states of excitons with n=2 and n=3. It should be noted that the Sommerfeld enhancement factor should be considered for a correct description of the behavior of the dielectric constant, taking into account excitonic effects.

Bulk Heterostructure BA2PbI4/MAPbI3 Perovskites for Suppressed Ion Migration To Achieve Sensitive X-ray Detection Performance

Three-dimensional (3D) lead-halide perovskites with outstanding mobility-lifetime products and large attenuation coefficients for X-ray photons have demonstrated highly sensitive X-ray detection. However, there exists severe ion migration, especially under electrical bias, that results in dark-current drift and poorer device stability. Theoretical analyses suggest that 3D perovskites with two-dimensional (2D) perovskites may mitigate ion migration and reduce the dark current to achieve a drastically lower detection limit, which is badly needed for X-ray diagnostics. A bulk 2D/3D perovskite heterostructure is therefore designed and prepared by hot-pressing a mixture of BA₂PbI₄ and MAPbI₃ particles. Compared with the pure MAPbI₃ pellet, the bulk 2D/3D heterostructure pellet shows much higher resistivity, hence, significantly reduced ion migration and a much smaller dark-current drift of 4.84 × 10^-5 nA cm^-1 s^-1 V^-1, which is much lower than that of the pristine MAPbI₃ pellet, thus demonstrating its effectiveness for the suppression of ion migration. The bulk 2D/3D heterostructure pellet attains an X-ray sensitivity of 2.0 × 10³ μC Gy_air^-1 cm^-2 as well as a lower detection limit of 111.76 nGy s^-1 under 10 V bias. This work provides a successful strategy to prepare X-ray detectors with suppressed ion migration and negligible dark current drift, which will further benefit the development of lead-halide perovskite X-ray detectors.

A Wide Bandgap Halide Perovskite Based Self-Powered Blue Photodetector with 84.9% of External Quantum Efficiency

A self-powered, color-filter-free blue photodetector (PD) based on halide perovskites is reported. A high external quantum efficiency (EQE) of 84.9%, which is the highest reported EQE in blue PDs, is achieved by engineering the A-site monovalent cations of wide-bandgap perovskites. The optimized composition of formamidinium (FA)/methylammonium (MA) increases the heat of formation, yielding a uniform and smooth film. The incorporation of Cs⁺ ions into the FA/MA composition suppresses the trap density and increases charge-carrier mobility, yielding the highest average EQE of 77.4%, responsivity of 0.280 A W^-1 , and detectivity of 5.08 × 10¹² Jones under blue light. Furthermore, Cs⁺ improves durability under repetitive operations and ambient atmosphere. The proposed device exhibits peak responsivity of 0.307 A W^-1 , which is higher than that of the commercial InGaN-based blue PD (0.289 A W^-1 ). This study will promote the development of next-generation image sensors with vertically stacked perovskite PDs.

Vertically Oriented Porous PET as Template to Integrated Metal Halide for High-Performance Large-Area and Ultra-Flexible X-Ray Detector

High-performance X-ray detectors have immense potential in medical and security inspections. However, the current X-ray detectors are limited in flexible, high-spatial-resolution large-scale detection, and integration for imaging. Here, nuclear track-etched porous polyethylene terephthalate (PET) is developed as the template for preparing uniform, large-area (≥10⁵ cm² ), and flexible metal halide (MH)-based X-ray detectors. Adjustable high-density vertically oriented porous PET with adjustable thickness can provide proper physical support for flexible thick absorption film, thus improving X-ray absorption ability with excellent bending stability. Moreover, vertical channels can block the ion migration, lateral charge diffusion, and water/oxygen attacks, increasing activation energy for ionic transport, charge collection rate of electrodes, and environmental stability. Hence, the related detectors eventually obtain large sensitivity (6722 µC Gy_air ^-1 cm^-2 ), low detection limit (1.87 nGy_air s^-1 ), and high spatial resolution (5.17 lp mm^-1 ) compared to the detectors without porous PET template. Meanwhile, the device shows no degradation after storage or working under various thermal attacks. MH-filled-PET is also monolithically integrated on the bottom circuit with different MHs and it is applied to single-pixel mode and fast linear-array imaging in a broad range of X-rays photon energy (20 to 160 keV).

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.

Room-temperature polariton quantum fluids in halide perovskites

Quantum fluids exhibit quantum mechanical effects at the macroscopic level, which contrast strongly with classical fluids. Gain-dissipative solid-state exciton-polaritons systems are promising emulation platforms for complex quantum fluid studies at elevated temperatures. Recently, halide perovskite polariton systems have emerged as materials with distinctive advantages over other room-temperature systems for future studies of topological physics, non-Abelian gauge fields, and spin-orbit interactions. However, the demonstration of nonlinear quantum hydrodynamics, such as superfluidity and Čerenkov flow, which is a consequence of the renormalized elementary excitation spectrum, remains elusive in halide perovskites. Here, using homogenous halide perovskites single crystals, we report, in both one- and two-dimensional cases, the complete set of quantum fluid phase transitions from normal classical fluids to scatterless polariton superfluids and supersonic fluids—all at room temperature, clear consequences of the Landau criterion. Specifically, the supersonic Čerenkov wave pattern was observed at room temperature. The experimental results are also in quantitative agreement with theoretical predictions from the dissipative Gross-Pitaevskii equation. Our results set the stage for exploring the rich non-equilibrium quantum fluid many-body physics at room temperature and also pave the way for important polaritonic device applications.

Mixed 3D-2D Perovskite Flexible Films for the Direct Detection of 5 MeV Protons

This study reports on a novel, flexible, proton beam detector based on mixed 3D-2D perovskite films deposited by solution onto thin plastic foils. The 3D-2D mixture allows to obtain micrometer-thick and highly uniform films that constitute the detector's active layer. The devices demonstrate excellent flexibility with stable electric transport properties down to a bending radius of 3.1 mm. The detector is characterized under a 5 MeV proton beam with fluxes in the range [4.5 × 105 - 1.4 × 109 ] H+ cm-2 s-1 , exhibiting a stable response to repetitive irradiation cycles with sensitivity up to (290 ± 40) nC Gy-1 mm-3 and a limit of detection down to (72±2) µGy s-1 . The detector radiation tolerance is also assessed up to a total of 1.7 × 1012 protons impinging on the beam spot area, with a maximum variation of the detector's response of 14%.

Dark current modeling of thick perovskite X-ray detectors

Metal halide perovskites (MHPs) have demonstrated excellent performances in detection of X-rays and gamma-rays. Most studies focus on improving the sensitivity of single-pixel MHP detectors. However, little work pays attention to the dark current, which is crucial for the back-end circuit integration. Herein, the requirement of dark current is quantitatively evaluated as low as 10^-9 A/cm² for X-ray imagers integrated on pixel circuits. Moreover, through the semiconductor device analysis and simulation, we reveal that the main current compositions of thick perovskite X-ray detectors are the thermionic-emission current (J_T) and the generation-recombination current (J_g-r). The typical observed failures of p-n junctions in thick detectors are caused by the high generation-recombination current due to the band mismatch and interface defects. This work provides a deep insight into the design of high sensitivity and low dark current perovskite X-ray detectors.

High-resolution flexible X-ray luminescence imaging enabled by eco-friendly CuI scintillators

Solution-processed scintillators hold great promise in fabrication of low-cost X-ray detectors. However, state of the art of these scintillators is still challenging in their environmental toxicity and instability. In this study, we develop a class of tetradecagonal CuI microcrystals as highly stable, eco-friendly, and low-cost scintillators that exhibit intense radioluminescence under X-ray irradiation. The red broadband emission is attributed to the recombination of self-trapped excitons in CuI microcrystals. We demonstrate the incorporation of such CuI microscintillator into a flexible polymer to fabricate an X-ray detector for high-resolution imaging with a spatial resolution up to 20 line pairs per millimeter (lp mm−1), which enables sharp image effects by attaching the flexible imaging detectors onto curved object surfaces.

Spray-coated perovskite hemispherical photodetector featuring narrow-band and wide-angle imaging

Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA₂FA_n-1Pb_nX_3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10^-4 cm³ s^-1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.

Low Trap Density Para-F Substituted 2D PEA2PbX4 (X = Cl, Br, I) Single Crystals with Tunable Optoelectrical Properties and High Sensitive X-Ray Detector Performance

Exploring halogen engineering is of great significance for reducing the density of defect states in crystals of organic-inorganic hybrid perovskites and hence improving the crystal quality. Herein, high-quality single crystals of PEA₂PbX₄ (X = Cl, Br, I) and their para-F (p-F) substitution analogs are prepared using the facile solution method to study the effects of both p-F substitution and halogen anion engineering. After p-F substitution, the triclinic PEA₂PbX₄ (X = Cl, Br) and cubic PEA₂PbX₄ (X = I) crystals unifies to monoclinic crystal structure for p-F-PEA₂PbX₄ (X = Cl, Br, I) crystals. The p-F substitution and halogen engineering, together with crystal structure variation, enable the tunability of optoelectrical properties. Experimentally, after the p-F substitution, the energy levels are lowered with increased Fermi levels, and the bandgaps of p-F-PEA₂PbX₄ (X = Cl, Br, I) are slightly reduced. Benefitting from the enhancement of the charge transfer and the reduced trap density by p-F substitution and halogen anion engineering, the average carrier lifetime of the p-F-PEA₂PbX₄ is obviously reduced. Compared with PEA₂PbI₄, the X-ray detector based on p-F-PEA₂PbI₄ perovskite single-crystal has a higher sensitivity of 119.79 μC Gy_air⁻¹·cm⁻². Moreover, the X-ray detector based on p-F-PEA₂PbI₄ single crystals exhibits higher radiation stability under high-dose X-ray irradiation, implying long-term operando stability.

Study of Annihilation Photon Pair Coincidence Time Resolution Using Prompt Photon Emissions in New Perovskite Bulk Crystals

Semiconductor-based radiation detectors can typically achieve better energy and spatial resolution when compared to scintillator-based detectors. However, if used for positron emission tomography (PET), semiconductor-based detectors normally cannot achieve excellent coincidence time resolution (CTR), due to the relatively slow charge carrier collection time limited by the carrier drift velocity. If we can collect prompt photons emitted from certain semiconductor materials, there are possibilities that the CTR can be greatly improved, and time-of-flight (ToF) capability can be achieved. In this paper, we studied the prompt photon emission (mainly Cherenkov luminescence) property and fast timing capability of cesium lead chloride (CsPbCl3) and cesium lead bromide (CsPbBr3), which are two new perovskite semiconductor materials. We also compared their performance with thallium bromide (TlBr), another semiconductor material that has already been studied for timing using its Cherenkov emissions. We performed coincidence measurements using silicon photomultipliers (SiPMs), and the full-width-at-half-maximum (FWHM) CTR acquired between a semiconductor sample crystal and a reference lutetium-yttrium oxyorthosilicate (LYSO) crystal (both with dimensions of 3 × 3 × 3 mm3) is 248 ± 8 ps for CsPbCl3, 440 ± 31 ps for CsPbBr3, and 343 ± 16 ps for TlBr. Deconvolving the contribution to CTR from the reference LYSO crystal (around 100 ps) and then multiplying by the square root of 2, the estimated CTR between two of the same semiconductor crystals was calculated as 324 ± 10 ps for CsPbCl3, 606 ± 43 ps for CsPbBr3 and 464 ± 22 ps for TlBr. This ToF capable CTR performance combined with an easily scalable crystal growth process, low cost and toxicity, as well as good energy resolution lead us to the conclusion that new perovskite materials such as CsPbCl3 and CsPbBr3 could be excellent candidates as PET detector materials.

Application of perovskites in bioimaging: the state-of-the-art and future developments

BACKGROUND

Recently, the development of perovskite-based nanocrystals for sustainable applications in bioimaging and clinical diagnostics have become a very active area of research. From 2D hybrid to zero-dimensional quantum dots (QDs), perovskites along with a variety of characteristic features, specifically non-linear optoelectronics properties, have attracted enormous research attention. These characteristics can be tuned by the type of cations or anions and their ratio used in host perovskites. Carrier doping and chemical modifications are additional alternatives to control optical and magnetism in radiodiagnostics.

AREA COVERED

This review begins by explaining the physical phenomena associated with luminescence or optical features of novel perovskites in diagnostic applications. Moreover, reported oxide, halide, doped, and QDs-based nanoprobes were elaborated. At last, the need for novel perovskite development, for example, persistent luminescent and low cytotoxicity is discussed, and the futuristic perspective of perovskites in clinical diagnostics with real-time demonstration is explained.

EXPERT OPINION

Our article concludes that hybrid perovskites, including metal-free, core-shell nanocomposites-based, and alloy-based perovskites, exhibit tunable bandgap and high photoluminescence quantum yields which ultimately result in high optical features. However, given limited understanding of ion transport mechanisms and dependency on environmental conditions of the perovskites, more research is needed.

γ-ray Radiation Hardness of CsPbBr3 Single Crystals and Single-Carrier Devices

The superior environmental stability of all-inorganic metal halide perovskites compared to their organic-inorganic counterparts makes them more promising in practical applications. Here, the stability of an archetypical all-inorganic CsPbBr₃ single crystal and its single-carrier devices under ⁶⁰Co γ-ray irradiation was investigated. The CsPbBr₃ single crystal itself shows ostensible hardness as its structural and optical properties present imperceptible changes even with a total ionizing dose of 800 krad. Unexpectedly, the single crystal-based single-carrier devices exhibit apparent dose-dependent hardness. The performance of the hole-only device suffers from more deterioration than the electron-only device under high irradiation doses (>400 krad). Our results reveal that such a discrepancy originates from the different influences of γ-ray irradiation-induced defects on the transport behaviors of holes and electrons in CsPbBr₃ single-crystal devices. These findings offer a new understanding of the interaction mechanism between γ-photons and all-inorganic metal halide perovskite-based devices.

Lithium Chloride-Substituted Methylammonium Lead Tribromide Perovskites for Dual γ/Neutron Sensing

Dual γ/neutron radiation sensors are a critical component of the nuclear security mission to prevent the proliferation of a special nuclear material (SNM). While high-performing semiconductors such as high purity germanium (HPGe) and CdZnTe (CZT) already exist in the nuclear security enterprise, their high cost and/or logistical burdens make widespread deployment difficult to achieve. Metal lead halide perovskites (MHPs) have attracted interest in recent years to address this challenge. In particular, methylammonium lead tribromide (CH₃NH₃PbBr₃, MAPbBr₃, or MAPB) has been widely evaluated for its radiation sensing capabilities. While previous studies have demonstrated low-energy X-ray and α particle sensing of MAPB-based detectors and several studies discuss the potential for γ ray sensing, neutron sensing of this material has been rarely explored. Here, we explore the incorporation of lithium in the form of LiCl into the MAPB structure to add thermal neutron sensitivity. Characterizations of the lithium-doped MAPB crystals demonstrate that quality growths are achievable with single crystals that exhibit high crystallinity, no phase change, and high macroscopic bulk quality. Finally, we report on the first demonstrated γ ray and thermal neutron sensing based on lithium-doped MAPB single crystals, which is a significant milestone in the development of 3D dual γ/neutron MHP sensors.