Detection of special nuclear materials (SNMs) is of vital importance in the prevention of nuclear terrorism and to secure states' national security. Neutron detection is a particularly useful tool to identify SNM, and neutron-sensitive scintillators have many promising properties, such as ease of use, good time resolution, and high detection efficiency. In this work, we develop highly stable, self-oriented, ultrafast 1D ZnO:Li (and codoped with Al, Ga, and In) nanorods (NRs) as thermal neutron-sensitive scintillators. Lithium-6 has high thermal neutron cross section for the (n, α) reaction in ZnO:Li scintillators which have a vertical nano array design greatly increasing the effective surface area and scintillation efficiency. Cost-effective low-temperature (95 °C) hydrothermal growth is used to obtain highly crystalline ZnO:Li nano scintillators by combining nuclear range data and electron transport mechanisms. Among the studies using low-temperature hydrothermal synthesis and a relatively low annealing temperature (≈350 °C) along with optimized NRs (length ≈ 5-8 μm, mean diameter ≈ 700 nm) for thermal neutron detection, this study reports the shortest scintillation decay time (≈ 470 ps) so far to the best of our knowledge. This nano array scintillator combines the advantages of a low-cost growth technique with environmentally friendly and widely available materials.

To be used as efficient alpha particle scintillator in the fields of nuclear security, nuclear nonproliferation and high-energy physics, scintillator screens must have high light output and fast decay properties. While there has been a great deal of progress in scintillation efficiency, achieving fast decay time properties are still a challenge. In this work, the near band edge (NBE) UV luminescence and alpha particle induced scintillation properties of vertically aligned densely packed ZnO nanorods (NRs) doped with Al, Ga, and In have been thoroughly investigated. The high crystalline hexagonal wurtzite structure with a strong orientation through the c-axis plane (002) and aspect ratios in the range 13–22 have been observed for all ZnO NRs. Electron paramagnetic resonance (EPR) analysis exhibited paramagnetic signals at g ≈ 1.96 for all ZnO NRs. A cost effective green hydrothermal synthesis technique was employed to grow well-aligned NRs. Using citrate as an additive acting as a strong reducing agent in the solution during the crystal growth, defects on the surface are significantly suppressed, thereby enhancing the NBE UV emission. Significantly higher NBE UV emission was observed from the top surface of ZnO NRs in cathodoluminescence (CL) microscopy. Results show that citrate assisted donor doping of ZnO NRs not only reduces the defect emission and NBE self-absorption, but also induces fast decay time ( 600–700 ps), which makes ZnO NRs a good candidate for fast alpha particle scintillator screens used in associated particle imaging for time and direction tagging of individual neutrons generated in D–T and D–D neutron generators.

In this study, the investigation of a Cs2AgBiBr6 single crystal (SC) / CsPbBr3 nanocrystals (NCs) film double perovskite/perovskite type-II novel heterojunction tailored for superior X-ray detection applications is presented. One of the main benefits of utilizing such a heterojunction is its built-in electric potential, which improves charge transport and reduces the dark current in the devices. By casting CsPbBr3 NCs onto polished Cs2AgBiBr6 SC, the Cs2AgBiBr6/CsPbBr3 double perovskite/ perovskite heterojunction is fabricated. The heterojunction X-ray detector exhibits reduced dark current and increased photocurrent compared to the pristine SC device. This enhancement of photocurrent can be attributed to efficient carrier generation and separation facilitated by appropriate band bending at the type-II heterojunction interface. The heterojunction device shows an X-ray sensitivity of 6 mu CGy(-1) cm(-2) at 0 V of applied bias, owing to the built-in potential across the heterojunction. Remarkably, at a -50 V bias, the sensitivity of the heterojunction device reached 857.8 mu CGy(-1) cm(-2), with a limit of detection of 312 nGy s(-1). Density functional theory (DFT) calculations provided further insights, revealing electron transfer from CsPbBr3 to Cs2AgBiBr6, thereby enhancing the X-ray sensitivity of the heterojunction device. These findings underscore the potential of Cs2AgBiBr6/CsPbBr3 heterojunctions for X-ray detection and optoelectronic applications.

Metal halide perovskites and organic semiconductors have attracted intense interest for ionizing radiation detection due to their advantages of strong attenuation, low leakage currents, synthetic versatility, and simple device manufacturing. These materials present opportunities to develop devices for safer medical imaging and dosimetry, sensing, shielding technologies for space exploration, and improved non‐invasive analysis for security, product inspection, and nuclear safety. However, there is currently a glaring lack of standard approaches for testing and reporting the performance of novel organic semiconductor and perovskite‐based materials and device architectures for radiation detection. This absence of standardization has resulted in a recent exponential increase in publications that lack consistency in both the experimental procedures used for characterization and the interpretation of performance parameters reported. In this Perspective, the major photophysics of organic semiconductors and perovskite materials under high‐energy radiation are summarized, with limitations in evaluating radiation detection performance using metrics designed for highly crystalline inorganic technologies discussed. Finally, key metrics and experimental details that are suggested for reporting in publications to improve reproducibility and enable large data set analysis are identified, noting these procedures are not intended as an exhaustive or definitive list, but rather as a milestone toward enabling improved standardization.

In this study, we investigate how modulating organic spacers in perovskites influences their X-ray detection performance and reveal the mechanism of low-dose detection with high sensitivity using femtosecond-transient absorption spectroscopy (fs-TAS). Particularly, we employ N,N,N',N'-tetramethyl-1,4-phenylenediammonium (TMPDA) and N,N-dimethylphenylene-p-diammonium (DPDA) as organic spacers to synthesize 2D perovskite single crystals (SCs). We find that DPDA-based SCs exhibit reduced interplanar spacing between inorganic layers, leading to increased lattice packing. Density functional theory (DFT) results indicate the reduced effective mass and lower lattice distortion in (DPDA)PbBr4 suppressing the formation of self-trapped exciton (STEs) and electron-phonon coupling and enhancing carrier delocalization in these SCs. Further, X-ray detection measurements reveal that (DPDA)PbBr4 demonstrates higher sensitivity than (TMPDA)PbBr4, attributed to its enhanced carrier delocalization, and higher mobility-lifetime product. The limit of detection (LoD) for (DPDA)PbBr4 is determined to be 13 nGy/s, significantly lower than both commercial detectors and state-of-the-art perovskite-based X-ray detectors. Furthermore, fs-TAS study reveals that (DPDA)PbBr4 crystals exhibit prolonged hot STE cooling and decay lifetimes, which directly correlate with their higher sensitivity. This study highlights the impact of organic spacers on X-ray detection performance, providing a framework for designing ultra-low LoD detectors essential for health and security applications.

Metal halide perovskite single crystals have demonstrated potential as excellent direct radiation detectors. However, the growth of high quality perovskite single crystals is challenging due to long growth times and spontaneous nucleation. In this study, we demonstrate the growth and optimisation of bulk charge transport properties in FAPbBr 3 single crystals (FPB SCs) with the use of the sulfonic zwitterionic additive 3-(Decyldimethylammonio)propanesulfonate inner salt (DPSI). A DPSI concentration of 10% was found to be ideal for growing high quality FPB SCs. The FPB SCs synthesised using 10% DPSI show a relatively high electron and hole mobility of 84 cm 2 V -1 s -1 and 30 cm 2 V -1 s -1 respectively and a high carrier mobility lifetime product of 2.9 ×10 -3 cm 2 V -1 . A high X-ray sensitivity of 1.1 × 10 3 μC Gy air -1 cm -2 is obtained from these devices when irradiated with a 50 kV X-ray source at an applied electric field of 100 V cm -1 . The device showed a low detection limit of 72 nGy s -1 and a low and stable leakage current of 30 nA cm -2 (2.7 nA). Preliminary α spectroscopy measurements carried out from a 241 Am α source show a resolvable α peak from 10% DPSI FPB SCs at -130 V and a mean rise time of 1.3 μs under a bias voltage of -30 V. Therefore, these devices show great potential to be used as high resolution α and γ-ray spectroscopic detectors.

Abstract We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

This article details work performed on the synthesis and characterization of an inorganic mixed-cation double halide perovskite, Cs2Ag.6Na.4In.85Bi.15Cl6 (CANIBIC). Single crystals have been created via a hydrothermal reaction, milled into a powder, and pressed into pellets, while nanocrystals have been directly synthesized via mechanosynthesis. A computational model is constructed to predict the X-ray diffraction pattern of CANIBIC; this model aligns very well with the X-ray diffraction pattern measured for CANIBIC crystal powder. This model can therefore be developed in the future as a tool to predict lattice parameters and crystal structures of other novel double-halide perovskites. Photoluminescence spectra obtained from each format show broad emission centered at 630 nm, as is typical for self-trapped exciton emission; self-trapped exciton emission is also confirmed by investigating photoluminescence intensity as a function of laser power. Nanocomposites are produced via the loading of nanocrystals of CANIBIC into PMMA. Although nanocomposite disks consisting of a small proportion of CANIBIC nanocrystals in PMMA have a smaller mass attenuation coefficient than a pressed pellet of CANIBIC, these disks have comparatively bright radioluminescence due to their optical transparency. These nanocomposite disks are therefore a particularly useful format for the practical use of the CANIBIC scintillator. A new mechanical synthesis model for sub 500 nm nanocrystals of the mixed-cation double perovskite Cs2Ag.6Na.4In.85Bi.15Cl6 is presented alongside to hydrothermally grown single crystals. The crystal structure, elemental composition, and scintillation properties of these materials are discussed alongside nanocomposites incorporating nanocrystals. These materials present a viable path for radiation detectors, as displayed by their responses to X-ray and gamma radiation.image

We present a study of the optical and electrical properties of (BA) 2 PbI 4 n=1 Ruddlesden-Popper (RP) phase polycrystalline perovskite X-ray detectors. (BA) 2 PbI 4 single crystals were prepared using a slow cooling method and were processed into a powder before being pressed into pellets. A X-ray detector was fabricated from the resulting polycrystalline perovskite pellet. Our preliminary results show that polycrystalline 2D perovskite (BA) 2 PbI 4 wafer-based X-ray detectors showed a high resistivity of 1.03 × 10 11 Ω·cm, leading to low dark current, making it an ideal candidate for use as an X-ray detector. In this study we will characterise the X-ray response of (BA) 2 PbI 4 polycrystalline X-ray detectors and compare their sensitivity with single-crystal perovskite devices. By optimising the polycrystalline material structure we will enhance the performance of our devices and create an ultra-sensitive and efficient X-ray detector.

The work here reported discusses spectroscopic alpha particles detection based on 2D hybrid perovskite (phenylethylammonium lead bromide, PEA 2 PbBr 4 ) single crystals and enlights its extension to thin film devices of thickness in the micrometer scale. Solution-processed active materials are demonstrated to exhibit temporal stability and extremely low dark current ($\lt10 \mathrm{pA}$) at high applied electric field (1000V/mm), thus making them valid option for spectroscopic radiation detection applications. Although thickness being considered a limitation, the high performance of these devices leads to resolving alpha particles $(5.5 \mathrm{MeV})$ from ${ }^{241} \mathrm{Am}$ radioactive isotope. We propose a comparison of physical properties and responses of single crystals and thin films on interdigitated pixels (channel length $30 \mu \mathrm{m}$), from which we extract a Hecht-like behaviour and holes mobility-lifetime product of both the configurations (1.52 $\pm 0.3 \times 10^{-5} \mathrm{~cm}^{2} / \mathrm{V}$ and 6.0 ± $0.7 \times 10^{-7} \mathrm{~cm}^{2} / \mathrm{V}$ respectively), these corresponding to the 2D-perovskite parameters obtained with optical techniques from previous works. As alpha particle spectroscopy is crucial for radiation detection and advancements in various fields, the results here reported open to a wide range of novel applications as thin films grant both high performance and interesting mechanical properties to be exploited for spectroscopy-grade detectors.

X-ray detection is critical for applications in medical diagnosis, industrial inspection, security checks, scientific inquiry and space exploration. Recent advances in materials science, electronics, manufacturing and artificial intelligence have greatly propelled the field forward. In this Review we examine fundamental principles and recent breakthroughs in X-ray detection and imaging technologies, with a focus on the interplay between electrical engineering techniques and X-ray-responsive materials. We highlight two primary approaches: semiconductor-based direct detection and scintillator-based indirect detection. We then discuss innovations such as photon-counting detectors and heterojunction phototransistors and emphasize the critical contributions of electrical engineering in the development of these cutting-edge detectors. Subsequently, we provide an overview of X-ray detection applications, ranging from biomedical imaging and resonant X-ray techniques for material analysis to nanometre-resolution circuit imaging. Finally, the Review summarizes future research directions, which encompass 3D and 4D X-ray imaging sensors, multispectral X-ray imaging and artificial intelligence-assisted medical image diagnosis. This Review examines fundamental principles and recent breakthroughs in X-ray detection and imaging technologies, with a focus on the interplay between electrical engineering techniques and materials science.

The current challenge of wearable/implantable personal dosimeters for medical diagnosis and radiotherapy applications is lack of suitable detector materials possessing both excellent detection performance and biocompatibility. Here, we report a solution-grown biocompatible organic single crystalline semiconductor (OSCS), 4-Hydroxyphenylacetic acid (4HPA), achieving real-time spectral detection of charged particles with single-particle sensitivity. Along in-plane direction, two-dimensional anisotropic 4HPA exhibits a large electron drift velocity of 5 × 10 5 cm s −1 at “radiation-mode” while maintaining a high resistivity of (1.28 ± 0.003) × 10 12 Ω·cm at “dark-mode” due to influence of dense π-π overlaps and high-energy L1 level. Therefore, 4HPA detectors exhibit the record spectra detection of charged particles among their organic counterparts, with energy resolution of 36%, ( μt ) e of (4.91 ± 0.07) × 10 −5 cm 2 V −1 , and detection time down to 3 ms. These detectors also show high X-ray detection sensitivity of 16,612 μC Gy abs −1 cm −3 , detection of limit of 20 nGy air s −1 , and long-term stability after 690 Gy air irradiation.

We report a facile, solvent-free surfactant-dependentmechanochemicalsynthesis of highly luminescent CsPbBr3 nanocrystals (NCs)and study their scintillation properties. A small amount of surfactantoleylamine (OAM) plays an important role in the two-step ball millingmethod to control the size and emission properties of the NCs. Thesolid-state synthesized perovskite NCs exhibit a high photoluminescencequantum yield (PLQY) of up to 88% with excellent stability. CsPbBr3 NCs capped with different amounts of surfactant were dispersedin toluene and mixed with polymethyl methacrylate (PMMA) polymer andcast into scintillator discs. With increasing concentration of OAMduring synthesis, the PL yield of CsPbBr3/PMMA nanocompositewas increased, which is attributed to reduced NC aggregation and PLquenching. We also varied the perovskite loading concentration inthe nanocomposite and studied the resulting emission properties. Themost intense PL emission was observed from the 2% perovskite-loadeddisc, while the 10% loaded disc exhibited the highest radioluminescence(RL) emission from 50 kV X-rays. The strong RL yield may be attributedto the deep penetration of X-rays into the composite, combined withthe large interaction cross-section of the X-rays with the high-Zatoms within the NCs. The nanocomposite disc shows an intense RL emissionpeak centered at 536 nm and a fast RL decay time of 29.4 ns. Further,we have demonstrated the X-ray imaging performance of a 10% CsPbBr3 NC-loaded nanocomposite disc.

We present work on the development of mixed-halide perovskite (CsPbCl x Br (1− x ) ) nanocrystal scintillators for X-ray detection applications. The effect of the varying the halide composition on the resulting peak emission and light yield is discussed, with the CsPbBr 3 materials displaying the greatest light yield. These perovskite nanocrystals were successfully loaded into PMMA, an inert plastic, at 2% mass weighting and the responses of these composites were compared to that of their colloidal dispersions. The composites were also characterised in terms of the radioluminescent light yield and decay response, alongside their X-ray sensitivity, in which the PMMA-CsPbBr 3 composites again outperformed the materials containing Cl − anions.

The fabrication of perovskite-polymer composites elevates the potential of perovskite-based radiation detectors. Combining the facile production of all-inorganic perovskite materials with the mechanical properties of a polymer can result in the convenient production of large-area, environmentally stable detectors. This work presents the fabrication and characterization of a novel hybrid material that has been created by mixing together the perovskite CsPbBr 3 with a polymer to produce a solid plastic composite. Test samples are polished pellets with metal contacts to enable direct detection via charge collection. IV-characterization data and photocurrent response data has been collected from a composite test device composed of ~8% perovskite material by weight. Bias sweeps have been performed and the dark current measured. X-ray illumination from a 70 kV source across a series of mA values demonstrates the clear linear response of the device over a range of dose-rates. Additionally, microCT and SEM imaging has been used to study the dispersion of CsPbBr 3 through the composite. This work lays the foundation for novel perovskite-polymer radiation detection devices through detector characterization and compositional analysis.

Perovskites are a fascinating and varied class of materials that have great potential in radiation detector technologies. Following their initial development by the PV and solid-state lighting communities, perovskites are being actively developed worldwide as both semiconductor and scintillator radiation detectors. Of particular interest are lead halide perovskites where the presence of high-Z atoms such as Cs and Pb provides high X-ray and gamma ray efficiency, combined with good charge transport. These materials can be relatively easily fabricated using either high temperature or solution processing methods, with CsPbBr 3 currently the leading perovskite material for high resolution gamma spectroscopy applications. Particularly rapid progress has also been made in the development of perovskite X-ray imaging detectors, which have demonstrated excellent X-ray sensitivity, stability, and imaging performance. Through the use of sintered polycrystalline perovskite thick films, large area imaging detectors can be realised that are approaching the performance of traditional imaging detector materials such as a-Se and CdTe.The almost infinite range of perovskite materials means that the field of perovskite radiation detectors continues to expand. Structured 2D and 1D perovskites offer many hybrid organic/inorganic materials that combine high resistivity and low dark currents with excellent radiation sensitivity. ‘Lead free' double perovskites also offer environmentally beneficial materials, many of which combine good semiconductor properties with remarkably high scintillation light yields.In this talk I will present an overview of the latest results from Surrey and our collaborators on perovskite radiation detectors, including semiconductor single crystal detectors for gamma spectroscopy and polycrystalline perovskites for X-ray imaging, plus some recent key results from perovskite scintillators.

EDITORIAL article Front. Phys., 05 July 2023Sec. Radiation Detectors and Imaging Volume 11 - 2023 | https://doi.org/10.3389/fphy.2023.1242329

We report a systematic comparison of the charge transport and radiation detection properties of inorganic and organic metal bromide single crystal perovskites. We studied the performance of Bridgman-grown CsPbBr 3 single crystals, together with solution-grown FAPbBr 3 and MAPbBr 3 single crystals. Laser time of flight is used to measure the drift mobilities for all samples, and we report a maxium mobility value of 121 ± 10 cm V −1 s −1 for CsPbBr 3 . Alpha particle measurements were used to assess the mobility-lifetime products, with values recorded in the range of 2 × 10 −4 cm 2 V −1 to 1 × 10 −3 cm 2 V −1 . Low temperature measurements showed an increase in bulk resistivity at temperatures down to 260 K, but no significant change to the drift mobilities. The overall performance of the Cs, FA and MA samples is compared and their potential for use in gamma spectroscopy measurements is discussed.

Layered metal halide perovskites have attracted enormous research attention over the last few years, befitting their unique optical and electronic properties. Low‐dimensional layered perovskites demonstrate great potential for various optoelectronic and sensing applications beyond photovoltaics. Herein, the recent progress and opportunities in 2D and quasi‐2D perovskites for light‐emitting diodes (LEDs), lasers, memristors, neuromorphic/synaptic applications, UV–vis photodetection, X‐ray detection, scintillators, and photocatalytic applications are reviewed. First, the crystal structure, characteristics, and fundamental properties of 2D layered perovskites are discussed. Recent efforts and developments of 2D and quasi‐2D metal halide perovskite for light‐emitting applications with excellent luminescence properties are reviewed. Unique properties of 2D perovskites, such as negligible leakage current due to restricted carrier transport, high stability, and hydrophobicity, make them viable for memristor devices. After discussing the memristor and neuromorphic devices using 2D perovskites, the outstanding performance of 2D perovskites in UV–vis photodetection including polarization‐sensitive photodetection is discussed. 2D perovskites recently proved as a superior candidate in X‐ray detection with high stability. Further, the scintillation properties of 2D perovskites for the detection of ionizing radiation are discussed. Finally, some of the very recent achievements and present future outlook, including exciting opportunities in this burgeoning field are highlighted.

Low-cost and low-temperature solution-processed halide perovskite single crystals show great potential in direct X-ray detection due to their large X-ray attenuation coefficient and efficient carrier generation and transport. Herein, we present solution-grown toxic lead-free Cu-doped Cs 3 Bi 2 Br 9 perovskite single crystals for highly sensitive X-ray detection and imaging. We fabricated a direct X-ray detector using a 2.5 mm thick Cu-Cs 3 Bi 2 Br 9 single crystal with a vertical structure of Au/ Cu-Cs 3 Bi 2 Br 9 /Au. Cu-Cs 3 Bi 2 Br 9 single crystal exhibit ultra-low dark current density of 2.5 pA mm -2 under an applied electric field of 8 V mm -1, which is significant as compared to other perovskite single crystals and high carrier mobility lifetime product (μτ) of 3.62 × 10 -4 cm 2 V -1 was obtained. A sensitivity of 264 μC ${\text{G}}{{\text{y}}_{{\text{air}}}}^{ - 1}{\text{c}}{{\text{m}}^{ - 2}}$ was achieved under irradiation of 30 kV X-ray and applied electric field of 40 Vmm -1 . The single crystal detector demonstrates an ultra-low limit of detection of 48 nGy/s, a fast response time (< 3 ms) with excellent operational and storage stability. We further studied the response of our X-ray detector under irradiation of clinical LINAC of 6 MV hard X-rays, which shows excellent dose monitoring capability.