Metal Halide Perovskite Nanosheet for X-ray High-Resolution Scintillation Imaging Screens

High-stability double perovskite scintillator for flexible X-ray imaging

Metal halide perovskites, as a new class of attractive and potential scintillators, are highly promising in X-ray imaging. However, their application is limited by the sensitivity to moisture and irradiation. To address this issue, we reported a 2D layered double perovskite material Cs4Cd1-xMnxBi2Cl12 that exhibits high stability both under ambient condition and under X-ray irradiation. Cs4Cd1-xMnxBi2Cl12 demonstrates superior scintillation performance, including excellent X-ray response linearity and a high light yield (∼34,450 photons/MeV). More importantly, the X-ray excited emission intensity maintains 92% and 94% of its original value after stored at ambient condition for over two years and after X-ray irradiation with a total dose of 11.4 Gy, respectively. By mixing with PDMS (polydimethylsiloxane), we have successfully produced a high-quality flexible film that can be bent freely while maintaining its excellent scintillation properties. The scintillating screen exhibits outstanding imaging ability with a spatial resolution of up to 16.7 line pairs per millimeter (lp/mm), also, the superiority of this scintillation screen in flexible X-ray imaging is demonstrated. These results indicate the huge potential of this high-stability double perovskite scintillator in X-ray imaging.

Zero-Dimensional Copper(I) Halide Microcrystals as Highly Efficient Scintillators for Flexible X-ray Imaging

Commercially available rare-earth-doped inorganic oxide materials have been widely applied as X-ray scintillators, but the fragile characteristics, high detection limit, and harsh preparation condition seriously restrict their wide applications. Furthermore, it remains a huge challenge to realize X-ray flexible imaging technology for real-time monitoring of the curving interface of complex devices. To address these issues, we herein report two isostructural cuprous halides of zero-dimensional (0D) [AEPipz]CuX3·X·H2O (AEPipz = N-aminoethylpiperazine, X = Br and I) with controllable size to nanosize crystal as highly efficient scintillators toward flexible X-ray imaging. These cuprous halides exhibit highly efficient cyan photoluminescence and radioluminescence emissions with the highest quantum yield of 92.1% and light yield of 62,400 photons MeV-1, respectively, surpassing most of the commercially available inorganic scintillators. Meanwhile, the ultralow detection limit of 95.7 nGyair s-1 was far below the X-ray dose required for diagnosis (5.5 μGyair s-1). More significantly, the flexible film is facilely assembled with excellent foldability and high crack resistance, which further acts as a scintillation screen achieving a high spatial resolution of 17.4 lp mm-1 in X-ray imaging, demonstrating the potential application in wearable radiation radiography. The combined advantages of high light yield, low detection limit, and excellent flexibility promote these 0D cuprous halides as the most promising X-ray scintillators.

Organic Cation Modulation in Manganese Halides to Optimize Crystallization Process and X-Ray Response Toward Large-Area Scintillator Screen

Manganese halides are one of the most potential candidates for large-area flat-panel detection owing to their biological safety and all-solution preparation. However, reducing photon scattering and enhancing the efficient luminescence of scintillator screens remains a challenge due to their uncontrollable crystallization and serious nonradiative recombination. Herein, an organic cation modulation is reported to control the crystallization process and enhance the luminescence properties of manganese halides. Given the industrial requirements of the X-ray flat-panel detector, the large-area A2MnBr4 screen (900 cm2) with excellent uniformity is blade-coated at 60 °C. Theoretical calculations and in situ measurements reveal that organic cations with larger steric hindrance can slow down the crystallization of the screen, thus neatening the crystal arrangement and reducing the photon scattering. Moreover, larger steric hindrance can also endow the material with higher exciton binding energy, which is beneficial for restraining nonradiative recombination. Therefore, the BPP2MnBr4 (BPP = C25H22P+) screen with larger steric hindrance exhibits a superior spatial resolution (>20 lp mm-1) and ultra-low detection limit (< 250 nGyair s-1). This is the first time steric hindrance modulation is used in blade-coated scintillator screens, and it believes this study will provide some guidance for the development of high-performance manganese halide scintillators.

Large-Area Transparent Antimony-Based Perovskite Glass for High-Resolution X-ray Imaging

Nonlead low-dimensional halide perovskites attract considerable attention as X-ray scintillators. However, most scintillation screens exhibit pronounced light scattering, which detrimentally reduces the quality of X-ray imaging. Herein, we employed a simple and straightforward solvent-free melt-quenching method to fabricate a large-area zero-dimension (0D) antimony-based perovskite transparent medium, namely (C20H20P)2SbCl5 (C20H20P+ = ethyltriphenylphosphine). The transparency is due to the large steric hindrance of C20H20P+, which hinders the formation of crystals during the quenching process, thus forming a glass with low refractive index and uniform structure. This medium exhibits a high transmittance exceeding 80% in the range of 450-800 nm and shows a large Stokes shift of 245 nm, thereby minimizing light scattering, mitigating self-absorption, and enhancing the clarity of X-ray imaging. Moreover, it exhibits a high radioluminescence light yield of ∼12,535 photons MeV-1 and displays a high X-ray spatial resolution of 30 lp mm-1 owing to its high transparency. This study presents an alternative candidate for achieving high-quality X-ray detection and extends the applicability of transparent perovskite scintillators.

Biocompatible Silica-Coated Europium-Doped CsPbBr3 Nanoparticles with Luminescence in Water for Zebrafish Bioimaging

Cesium lead halide (CsPbX3, X = Br, Cl, and I) nanocrystals (NCs) are widely concerned and applied in many fields due to the excellent photoelectric performance. However, the toxicity of Pb and the loss of luminescence in water limit its application in vivo. A stable perovskite nanomaterial with good bioimaging properties is developed by incorporating europium (Eu) in CsPbX3 NCs followed with the surface coating of silica (SiO2) shell (CsPbX3:Eu@SiO2). Through the surface coating of SiO2, the luminescence stability of CsPbBr3 in water is improved and the leakage of Pb2+ is significantly reduced. In particular, Eu doping inhibits the photoluminescence quantum yield reduction of CsPbBr3 caused by SiO2 coating, and further reduces the release of Pb2+. CsPbBr3:Eu@SiO2 nanoparticles (NPs) show efficient luminescence in water and good biocompatibility to achieve cell imaging. More importantly, CsPb(ClBr)3:Eu@SiO2 NPs are obtained by adjusting the halogen components, and green light and blue light are realized in zebrafish imaging, showing good imaging effect and biosafety. The work provides a strategy for advanced perovskite nanomaterials toward biological practical application.

Bright and durable scintillation from colloidal quantum shells

Efficient, fast, and robust scintillators for ionizing radiation detection are crucial in various fields, including medical diagnostics, defense, and particle physics. However, traditional scintillator technologies face challenges in simultaneously achieving optimal performance and high-speed operation. Herein we introduce colloidal quantum shell heterostructures as X-ray and electron scintillators, combining efficiency, speed, and durability. Quantum shells exhibit light yields up to 70,000 photons MeV-1 at room temperature, enabled by their high multiexciton radiative efficiency thanks to long Auger-Meitner lifetimes (>10 ns). Radioluminescence is fast, with lifetimes of 2.5 ns and sub-100 ps rise times. Additionally, quantum shells do not exhibit afterglow and maintain stable scintillation even under high X-ray doses (>109 Gy). Furthermore, we showcase quantum shells for X-ray imaging achieving a spatial resolution as high as 28 line pairs per millimeter. Overall, efficient, fast, and durable scintillation make quantum shells appealing in applications ranging from ultrafast radiation detection to high-resolution imaging.

Cold-Sintered All-Inorganic Perovskite Bulk Composite Scintillators for Efficient X-ray Imaging

Cost-effective bulk scintillators with high density, large-area, and long-term stability are desirable for high-energy radiation detections. Conventional bulk polycrystalline or single-crystal scintillators are generally synthesized by high-temperature approaches, and it is challenging to realize simultaneously high detectivity/responsivity, spatial resolution, and rapid time response. Here, we report the cold sintering of bulk scintillators (at 90 °C) based on an "emitter-in-matrix" principle, in which emissive CsPbBr3 nanocrystals are embedded in a durable and transparent Cs4PbBr6 matrix. These bulk scintillators exhibit high light yield (33,800 photons MeV-1), low detection limit (79 nGyair s-1), fast decay time (9.8 ns), and outstanding spatial resolution of 8.9 lp mm-1 to X-ray radiation and an energy resolution of 19.3% for γ-ray (59.6 keV) detection. The composite scintillator also shows exceptional stability against environmental degradation and cyclic X-ray radiation. Our results demonstrate a cost-effective strategy for developing perovskite-based bulk transparent scintillators with exceptional performance and high radioluminescence stability for high-energy radiation detection and imaging.

Capillary Manganese Halide Needle-Like Array Scintillator with Isolated Light Crosstalk for Micro-X-Ray Imaging

The exacerbation of inherent light scattering with increasing scintillator thickness poses a major challenge for balancing the thickness-dependent spatial resolution and scintillation brightness in X-ray imaging scintillators. Herein, a thick pixelated needle-like array scintillator capable of micrometer resolution is fabricated via waveguide structure engineering. Specifically, this involves integrating a straightforward low-temperature melting process of manganese halide with an aluminum-clad capillary template. In this waveguide structure, the oriented scintillation photons propagate along the well-aligned scintillator and are confined within individual pixels by the aluminum reflective cladding, as substantiated from the comprehensive analysis including laser diffraction experiments. Consequently, thanks to isolated light-crosstalk channels and robust light output due to increased thickness, ultrahigh spatial resolutions of 60.8 and 51.7 lp mm-1 at a modulation transfer function (MTF) of 0.2 are achieved on 0.5 mm and even 1 mm thick scintillators, respectively, which both exceed the pore diameter of the capillary arrays' template (Φ = 10 µm). As far as it is known, these micrometer resolutions are among the highest reported metal halide scintillators and are never demonstrated on such thick scintillators. Here an avenue is presented to the demand for thick scintillators in high-resolution X-ray imaging across diverse scientific and practical fields.

Toward "super-scintillation" with nanomaterials and nanophotonics

Following the discovery of X-rays, scintillators are commonly used as high-energy radiation sensors in diagnostic medical imaging, high-energy physics, astrophysics, environmental radiation monitoring, and security inspections. Conventional scintillators face intrinsic limitations including a low extraction efficiency of scintillated light and a low emission rate, leading to efficiencies that are less than 10 % for commercial scintillators. Overcoming these limitations will require new materials including scintillating nanomaterials ("nanoscintillators"), as well as new photonic approaches that increase the efficiency of the scintillation process, increase the emission rate of materials, and control the directivity of the scintillated light. In this perspective, we describe emerging nanoscintillating materials and three nanophotonic platforms: (i) plasmonic nanoresonators, (ii) photonic crystals, and (iii) high-Q metasurfaces that could enable high performance scintillators. We further discuss how a combination of nanoscintillators and photonic structures can yield a "super scintillator" enabling ultimate spatio-temporal resolution while enabling a significant boost in the extracted scintillation emission.

The Electronic Impact of Light-Induced Degradation in CsPbBr3 Perovskite Nanocrystals at Gold Interfaces

The understanding of the interfacial properties in perovskite devices under irradiation is crucial for their engineering. In this study we show how the electronic structure of the interface between CsPbBr3 perovskite nanocrystals (PNCs) and Au is affected by irradiation of X-rays, near-infrared (NIR), and ultraviolet (UV) light. The effects of X-ray and light exposure could be differentiated by employing low-dose X-ray photoelectron spectroscopy (XPS). Apart from the common degradation product of metallic lead (Pb0), a new intermediate component (Pbint) was identified in the Pb 4f XPS spectra after exposure to high intensity X-rays or UV light. The Pbint component is determined to be monolayer metallic Pb on-top of the Au substrate from underpotential deposition (UPD) of Pb induced from the breaking of the perovskite structure allowing for migration of Pb2+.

Transparent and Planar Cs3Cu2Cl5 Crystals for Micrometer-Resolution X-ray Imaging Screen

Copper-based (I) halide perovskites have emerged as a promising candidate for scintillation screens in X-ray inspection and imaging areas due to their solution processability and high light yield. Here, a centimeter-sized Cs3Cu2Cl5 single crystal was grown by a slow-cooling method. The planar orientation was controlled in a space-confined chamber, generating a planar crystal which is readily used for a scintillation screen without any further shaping. The crystal exhibited a unity photoluminescence quantum yield and superior scintillation performance. The Cs3Cu2Cl5 single crystal exhibited a high light yield up to 95,000 photons/MeV, which enabled an X-ray detector of a detection limit down to 2.7 μGyair/s. The homemade imager demonstrated a spatial resolution of 105 lp/mm, representing an unprecedented micrometer resolution in laboratory. Importantly, the stability of Cs3Cu2Cl5 was significantly improved by a new surface passivation procedure, whereby the passivated crystal reserved its phase after 6 months' storage in a vial. This work introduced a new solution-based synthetic method for two-dimensional scintillating crystals, opening many avenues to high-performance X-ray imaging applications.

A 0D hybrid lead-free halide with near-unity photoluminescence quantum yield toward multifunctional optoelectronic applications

Zero-dimensional (0D) hybrid metal halides have emerged as highly efficient luminescent materials, but integrated multifunction in a structural platform remains a significant challenge. Herein, a new hybrid 0D indium halide of (Im-BDMPA)InCl6·H2O was designed as a highly efficient luminescent emitter and X-ray scintillator toward multiple optoelectronic applications. Specifically, it displays strong broadband yellow light emission with near-unity photoluminescence quantum yield (PLQY) through Sb3+ doping, acting as a down-conversion phosphor to fabricate high-performance white light emitting diodes (WLEDs). Benefiting from the high PLQY and negligible self-absorption characteristics, this halide exhibits extraordinary X-ray scintillation performance with a high light yield of 55 320 photons per MeV, which represents a new scintillator in 0D hybrid indium halides. Further combined merits of a low detection limit (0.0853 μGyair s-1), ultra-high spatial resolution of 17.25 lp per mm and negligible afterglow time (0.48 ms) demonstrate its excellent application prospects in X-ray imaging. In addition, this 0D halide also exhibits reversible luminescence off-on switching toward tribromomethane (TBM) but fails in any other organic solvents with an ultra-low detection limit of 0.1 ppm, acting as a perfect real-time fluorescent probe to detect TBM with ultrahigh sensitivity, selectivity and repeatability. Therefore, this work highlights the multiple optoelectronic applications of 0D hybrid lead-free halides in white LEDs, X-ray scintillation, fluorescence sensors, etc.

Sb-Doped Cs3 TbCl6 Nanocrystals for Highly Efficient Narrow-Band Green Emission and X-Ray Imaging

Metal halide nanocrystals (NCs) with high photoluminescence quantum yield (PLQY) are desirable for lighting, display, and X-ray detection. Herein, the novel lanthanide-based halide NCs are committed to designing and optimizing the optical and scintillating properties, so as to unravel the PL origin, exciton dynamics, and optoelectronic applications. Sb-doped zero-dimensional (0D) Cs3 TbCl6 NCs exhibit a green emission with a narrow full width of half maximum of 8.6 nm, and the best PLQY of 48.1% is about three times higher than that of undoped NCs. Experiments and theoretical calculations indicate that 0D crystalline and electronic structures make the exciton highly localized on [TbCl6 ]3- octahedron, which boosts the Cl- -Tb3+ charge transfer process, thus resulting in bright Tb3+ emission. More importantly, the introduction of Sb3+ not only facilitates the photon absorption transition, but also builds an effective thermally boosting energy transfer channel assisted by [SbCl6 ]3- -induced self-trapped state, which is responsible for the PL enhancement. The high luminescence efficiency and negligible self-absorption of the Cs3 TbCl6 : Sb nanoscintillator enable a more sensitive X-ray detection response compared with undoped sample. The study opens a new perspective to deeply understand the excited state dynamics of metal halide NCs, which helps to design high-performance luminescent lanthanide-based nanomaterials.

Robust Organogel Scintillator for Self-healing and Ultra-flexible X-ray Imaging

Metal halide scintillators serve as promising candidates for X-ray detection due to their high attenuation coefficients, high light yields, and low-cost solution-processable characteristics. However, the issues of humidity/thermal quenching and mechanical fragility, remain obstacles to the broad and diversified development of metal halide scintillators. Here, this work reports a lead-free, water-stable, stretchable, and self-healing (ethylenebis-triphenylphosphonium manganese (II) bromide (C38 H34 P2 )MnBr4 organogel scintillator that meets X-ray imaging in complex scenarios. The robust organogel scintillator can be stretched with elongation up to 1300% while maintaining the scintillation properties. Activated by the dynamic hydrogen bonds and coordination bonds design, the organogel scintillator exhibits excellent self-healing properties at room temperature to alleviate the vignetting problem of the rigid scintillator films, the X-ray imaging resolution can reach 16.7 lp mm-1 . The organogel scintillator can also realize flexible and self-healing X-ray imaging in water, providing a design path for portable devices in harsh conditions.

Ligand Engineering Enables Efficient Pure Red Tin-Based Perovskite Light-Emitting Diodes

With increasing ecological and environmental concerns, tin (Sn)-based perovskite light-emitting diodes (PeLEDs) are competitive candidates for future displays because of their environmental friendliness, excellent photoelectric properties, and low-cost solution-processed fabrication. Nonetheless, their electroluminescence (EL) performance still lags behind that of lead (Pb)-based PeLEDs due to the fast crystallization rate of Sn-based perovskite films and undesired oxidation from Sn2+ to Sn4+ , leading to poor film morphology and coverage, as well as high density defects. Here, we propose a ligand engineering strategy to construct high-quality phenethylammonium tin iodide (PEA2 SnI4 ) perovskite films by using L-glutathione reduced (GSH) as surface ligands toward efficient pure red PEA2 SnI4 -based PeLEDs. We show that the hydrogen-bond and coordinate interactions between GSH and PEA2 SnI4 effectively reduce the crystallization rate of the perovskites and suppress the oxidation of Sn2+ and formation of defects. The improved pure red perovskite films not only show excellent uniformity, density, and coverage but also exhibit enhanced optical properties and stability. Finally, state-of-the-art pure red PeLEDs achieve a record external quantum efficiency of 9.32 % in the field of PEA2 SnI4 -based devices. This work demonstrates that ligand engineering represents a feasible route to enhance the EL performance of Sn-based PeLEDs.

Pressure-Induced Superconductivity and Topological Quantum Phase Transitions in the Topological Semimetal ZrTe2

Topological transition metal dichalcogenides (TMDCs) have attracted much attention due to their potential applications in spintronics and quantum computations. In this work, the structural and electronic properties of topological TMDCs candidate ZrTe2 are systematically investigated under high pressure. A pressure-induced Lifshitz transition is evidenced by the change of charge carrier type as well as the Fermi surface. Superconductivity is observed at around 8.3 GPa without structural phase transition. A typical dome-shape phase diagram is obtained with the maximum Tc of 5.6 K for ZrTe2 . Furthermore, the theoretical calculations suggest the presence of multiple pressure-induced topological quantum phase transitions, which coexists with emergence of superconductivity. The results demonstrate that ZrTe2 with nontrivial topology of electronic states displays new ground states upon compression.

Aqueous-Based Inorganic Colloidal Halide Perovskites Customizing Liquid Scintillators

Compared to solid scintillators and organic liquid scintillators, aqueous-based liquid scintillators (AbLS) have more superiority in highly flexible scalability, yet are now limited by their low light yield (≈100 photons MeV-1 ). Here, aqueous-based inorganic colloidal halide perovskites with high photoluminescence quantum yield (PLQY) of three primary color luminescence up to 88.1% (red), 96% (green), and 81.8% (blue) are respectively synthesized, and a new generation of colloidal perovskite-mediated AbLS (PAbLS) with light yield increased in comparison with the commercial scintillator AbLS is fabricated. This paper exhibits that the excellent PLQY and colloidal dispersion of halide perovskites benefit from poly(ethylene glycol) modification and this modification ensures the vacancy inhibition and formation of defect-free surfaces in an aqueous solution. Moreover, their high luminescent emission can be maintained for 100 days at low temperatures, and such modification also promises the heat-to-cold customization of operating temperature even in ice below 0 °C. Finally, depending on the light yield of around 3058 and 8037 photons MeV-1 at room temperature and low temperature, PAbLS with shape/size scalability exhibit their robust radiation hardness (dose rate as high as 23 mGy s-1 ) and conceptual application potential in high-energy ray radiation detection from every angle of 360°.

Yellow Emissive CsCu2I3 Nanocrystals Induced by Mn2+ for High-Resolution X-ray Imaging

Recently, low-dimensional copper(I)-based perovskite or derivatives have gained extensive attention in scintillator applications because of their environmental friendliness and good stabilities. However, the unsatisfactory scintillation performance and complex fabrication processes hindered their practical applications. Herein, efficient yellow emissive CsCu2I3 nanocrystals (NCs) were successfully prepared via a simple Mn2+-assisted hot-injection method. The added Mn2+ effectively induced the phase transformation from Cs3Cu2I5 to CsCu2I3, leading to the preparation of single-phase CsCu2I3 NCs with few defects and a high fluorescence performance. The as-prepared "optimal CsCu2I3 NCs" exhibited superior photoluminescence (PL) performance with a record-high PL quantum yield (PLQY) of 61.9%. The excellent fluorescence originated from the radiative recombination of strongly localized one-dimension (1D) self-trapped excitons (STEs), which was systematically investigated via the wavelength-dependent PL excitation, PL emission, and temperature-dependent PL spectra. These CsCu2I3 NCs also exhibited outstanding X-ray scintillation properties with a high light yield (32000 photons MeV-1) and an ultralow detection limit (80.2 nGyair s-1). Eventually, the CsCu2I3 NCs scintillator film achieved an ultrahigh (16.6 lp mm-1) spatial resolution in X-ray imaging. The CsCu2I3 NCs also exhibited good stabilities against X-ray irradiation, heat, and environmental storage, indicating their great application potential in flexible X-ray detection and imaging.

0D hybrid indium halide as a highly efficient X-ray scintillation and ultra-sensitive fluorescent probe

Halide perovskite nanocrystal (PNC) of 3D CsPbX3 as a scintillator has aroused intensive attention with advanced applications in radiation detection and X-ray imaging. However, the low light yield and serious toxicity of Pb2+ severely hinder advanced optoelectronic applications. To reduce these fatal shortcomings, a family of new environmentally friendly 0D hybrid lead-free indium halides of [DADPA]InX6·H2O (DADPA = 3,3'-diaminodipropylamine; X = Cl and Br) was prepared. Upon UV excitation, these halides display strong broadband yellow-orange light emissions, and the photoluminescence quantum yield (PLQY) can be optimized up to near unity through the Sb3+-doping strategy. Significantly, high PLQY, negligible self-absorption and low attenuation ability toward X-ray render extraordinary scintillation performance with a high light yield of 51 875 photons MeV-1 and ultralow detection limit of 98.3 nGyair s-1, which is far superior to typical 3D PNC scintillators. Additionally, the ultra-high spatial resolution of 25.15 lp mm-1, negligible afterglow time (2.75 ms) and robust radiant stability demonstrates excellent X-ray imaging performance. To the best of our knowledge, this is the first report on X-ray scintillation based on 0D indium halide materials.

A ligand strategy retarding monovalent copper oxidation toward achieving Cs3Cu2I5 perovskite emitters with enhanced stability for lighting

0D copper-based perovskites (Cs3Cu2I5) have fascinating optical properties, such as strong exciton binding energy, high photoluminescence quantum yield (PLQY) and large Stokes shifts from self-trapped excitons (STEs), which make them highly considerable candidates in the field of lighting. However, the stability of Cs3Cu2I5 is compromised by the oxidation of Cu+ to Cu2+ during the storage or operation process. Here, we proposed a ligand engineering strategy to improve the stability of Cs3Cu2I5via an organic molecule (ethylenediaminetetraacetic acid, EDTA) with multiple functional groups. The strong interaction between carboxyl groups and Cu+ was evidenced through FTIR and XPS, and it could retard monovalent copper oxidation. After storing for 90 days, the EDTA-engineered Cs3Cu2I5 (EDTA-Cs3Cu2I5) maintained its original crystalline structure, while the control Cs3Cu2I5 exhibited an impurity phase. Through quantitative analysis, the content of Cu2+ in EDTA-Cs3Cu2I5 was found to be 83.9% lower than that in control Cs3Cu2I5. Benefiting from the inhibition of Cu+ oxidation, EDTA-Cs3Cu2I5 exhibited improved light emission stability. For example, the optimized EDTA-Cs3Cu2I5 retained 74.7% of the initial photoluminescence (PL) intensity after 90-day storage under ambient conditions, while the pure Cs3Cu2I5 retained only 41.7%. Furthermore, EDTA could passivate defects and enhance the PL properties of the optimized Cs3Cu2I5, which showed a PLQY of 94.7%, much higher than that of 71.4% for pure Cs3Cu2I5. We further constructed a WLED based on the EDTA-engineered Cs3Cu2I5, which showed CIE at (0.3238, 0.3354), a CRI of 91.7, and a T50 of 361 h. The proposed EDTA ligand strategy provides a new way to regulate the light-emitting properties and stabilities of Cs3Cu2I5 for future industrialization.

Cascade perovskite single crystal for gamma-ray spectroscopy

The halide lead perovskite single crystals (HLPSCs) have great potential in gamma-ray detection with high attenuation coefficient, strong defects tolerance, and large mobility-lifetime product. However, mobile halide ions would migrate under high external bias, which would both weaken the gamma-ray response and cause additional noise. Here, we report the gamma-ray PIN photodiodes made of cascade HLPSCs including both ion-formed and electron-hole-formed electrical junctions that could suppress the ions migration and improve the charges collection. Our photodiodes based on cascade HLPSCs (MAPbBr3/MAPbBr2.5Cl0.5/MAPbCl3) show a wide halide-ion-formed depletion layer of ∼52 μm. The built-in potential along the wide ionic-formed junction ensures a high mobility-lifetime product of 1.1 × 10-2 cm2V-1. As a result, our gamma-ray PIN photodiodes exhibit compelling response to 241Am, 137Cs, and 60Co; the energy resolution can reach 9.4%@59.5keV and 5.9%@662keV, respectively. This work provides a new path toward constructing high-performance gamma-ray detectors based on HLPSCs.

Perovskite Scintillators for Improved X-ray Detection and Imaging

Halide perovskites (HPs) recently have emerged as one class of competitive scintillators for X-ray detection and imaging owing to its high quantum efficiency, short decay time, superior X-ray absorption capacity, low cost, and ease of crystal growth. The tunable structure and versatile chemical compositions of halide perovskites provide distinguishable advantages over traditional inorganic scintillators for optimizing scintillation performance. Since the first observation of the scintillation phenomenon in HPs, substantial efforts have been devoted to expanding the inventory of HP scintillators and regulating material properties. Understanding the relationship between the structure and scintillation properties of HP scintillators is essential for developing materials with improved X-ray detection and imaging capacities. This review summarizes strategies for improving the light yield of HP scintillators and provides a roadmap for improving the X-ray imaging performance. Additionally, methods for controlling the light propagation direction in HP scintillators are highlighted for improving X-ray imaging resolution. Finally, we highlight the current challenge in HP scintillators and provide a perspective on the future development of this emerging scintillator.

Surfactant-Dependent Bulk Scale Mechanochemical Synthesis of CsPbBr3 Nanocrystals for Plastic Scintillator-Based X-ray Imaging

We report a facile, solvent-free surfactant-dependent mechanochemical synthesis of highly luminescent CsPbBr3 nanocrystals (NCs) and study their scintillation properties. A small amount of surfactant oleylamine (OAM) plays an important role in the two-step ball milling method to control the size and emission properties of the NCs. The solid-state synthesized perovskite NCs exhibit a high photoluminescence quantum yield (PLQY) of up to 88% with excellent stability. CsPbBr3 NCs capped with different amounts of surfactant were dispersed in toluene and mixed with polymethyl methacrylate (PMMA) polymer and cast into scintillator discs. With increasing concentration of OAM during synthesis, the PL yield of CsPbBr3/PMMA nanocomposite was increased, which is attributed to reduced NC aggregation and PL quenching. We also varied the perovskite loading concentration in the nanocomposite and studied the resulting emission properties. The most intense PL emission was observed from the 2% perovskite-loaded disc, while the 10% loaded disc exhibited the highest radioluminescence (RL) emission from 50 kV X-rays. The strong RL yield may be attributed to the deep penetration of X-rays into the composite, combined with the large interaction cross-section of the X-rays with the high-Z atoms within the NCs. The nanocomposite disc shows an intense RL emission peak 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.

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.

Review of nanomaterial advances for ionizing radiation dosimetry

There are a wide range of applications with ionizing radiation and a common theme throughout these is that accurate dosimetry is usually required, although many newer demands are provided by improved features in higher range, multi-spectral and particle type detected. Today, the array of dosimeters includes both offline and online tools, such as gel dosimeters, thermoluminescence (TL), scintillators, optically stimulated luminescence (OSL), radiochromic polymeric films, gels, ionization chambers, colorimetry, and electron spin resonance (ESR) measurement systems. Several future nanocomposite features and interpretation of their substantial behaviors are discussed that can lead to improvements in specific features, such as (1) lower sensitivity range, (2) less saturation at high range, (3) overall increased dynamic range, (4) superior linearity, (5) linear energy transfer and energy independence, (6) lower cost, (7) higher ease of use, and (8) improved tissue equivalence. Nanophase versions of TL and ESR dosimeters and scintillators each have potential for higher range of linearity, sometimes due to superior charge transfer to the trapping center. Both OSL and ESR detection of nanomaterials can have increased dose sensitivity because of their higher readout sensitivity with nanoscale sensing. New nanocrystalline scintillators, such as perovskite, have fundamentally important advantages in sensitivity and purposeful design for key new applications. Nanoparticle plasmon coupled sensors doped within a lower Zeff material have been an effective way to achieve enhanced sensitivity of many dosimetry systems while still achieving tissue equivalency. These nanomaterial processing techniques and unique combinations of them are key steps that lead to the advanced features. Each must be realized through industrial production and quality control with packaging into dosimetry systems that maximize stability and reproducibility. Ultimately, recommendations for future work in this field of radiation dosimetry were summarized throughout the review.

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

Lead halide perovskites have recently emerged as promising X/γ-ray scintillators. However, the small Stokes shift of exciton luminescence in perovskite scintillators creates problems for the light extraction efficiency and severely impedes their applications in hard X/γ-ray detection. Dopants have been used to shift the emission wavelength, but the radioluminescence lifetime has also been unwantedly extended. Herein, we demonstrate the intrinsic strain in 2D perovskite crystals as a general phenomenon, which could be utilized as self-wavelength shifting to reduce the self-absorption effect without sacrificing the radiation response speed. Furthermore, we successfully demonstrated the first imaging reconstruction by perovskites for application of positron emission tomography. The coincidence time resolution for the optimized perovskite single crystals (4 × 4 × 0.8 mm³) reached 119 ± 3 ps. This work provides a new paradigm for suppressing the self-absorption effect in scintillators and may facilitate the application of perovskite scintillators in practical hard X/γ-ray detections.

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.

Sub-Nanosecond 2D Perovskite Scintillators by Dielectric Engineering

Perovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub-nanosecond region, while sub-nanosecond scintillators are highly demanded in various radiation detection, including high speed X-ray imaging, time-of-flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb-Br octahedral emitters in 2D organic-inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr₆ ]^2- layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM₂ PbBr₄ . The emitting decay time is shortened as 0.97 ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190 photons MeV^-1 , which is greatly higher than conventional ultrafast scintillator BaF₂ (1500 photons MeV^-1 ). The rare combination of ultrafast decay time and considerable light yield renders BM₂ PbBr₄ excellent performance in γ-ray, neutron, α-particle detection, and the best theoretical coincidence time resolution of 65.1 ps, which is only half of the reference sample LYSO (141.3 ps).

Copper Organometallic Iodide Arrays for Efficient X-ray Imaging Scintillators

Lead-free organic metal halide scintillators with low-dimensional electronic structures have demonstrated great potential in X-ray detection and imaging due to their excellent optoelectronic properties. Herein, the zero-dimensional organic copper halide (18-crown-6)₂Na₂(H₂O)₃Cu₄I₆ (CNCI) which exhibits negligible self-absorption and near-unity green-light emission was successfully deployed into X-ray imaging scintillators with outstanding X-ray sensitivity and imaging resolution. In particular, we fabricated a CNCI/polymer composite scintillator with an ultrahigh light yield of ∼109,000 photons/MeV, representing one of the highest values reported so far for scintillation materials. In addition, an ultralow detection limit of 59.4 nGy/s was achieved, which is approximately 92 times lower than the dosage for a standard medical examination. Moreover, the spatial imaging resolution of the CNCI scintillator was further improved by using a silicon template due to the wave-guiding of light through CNCI-filled pores. The pixelated CNCI-silicon array scintillation screen displays an impressive spatial resolution of 24.8 line pairs per millimeter (lp/mm) compared to the resolution of 16.3 lp/mm for CNCI-polymer film screens, representing the highest resolutions reported so far for organometallic-based X-ray imaging screens. This design represents a new approach to fabricating high-performance X-ray imaging scintillators based on organic metal halides for applications in medical radiography and security screening.

Singlet Fission-Based High-Resolution X-Ray Imaging Scintillation Screens

X-ray imaging technology is critical to numerous different walks of daily life, ranging from medical radiography and security screening all the way to high-energy physics. Although several organic chromophores are fabricated and tested as X-ray imaging scintillators, they generally show poor scintillation performance due to their weak X-ray absorption cross-section and inefficient exciton utilization efficiency. Here, a singlet fission-based high-performance organic X-ray imaging scintillator with near unity exciton utilization efficiency is presented. Interestingly, it is found that the X-ray sensitivity and imaging resolution of the singlet fission-based scintillator are dramatically improved by an efficient energy transfer from a thermally activated delayed fluorescence (TADF) sensitizer, in which both singlet and triplet excitons can be efficiently harnessed. The fabricated singlet fission-based scintillator exhibits a high X-ray imaging resolution of 27.5 line pairs per millimeter (lp mm^-1 ), which exceeds that of most commercial scintillators, demonstrating its high potential use in medical radiography and security inspection.

Large Scale BN-perovskite Nanocomposite Aerogel Scintillator for Thermal Neutron Detection

State-of-the-art thermal neutron scintillation detectors rely on rare isotopes for neutron capture, lack stability and scalability of solid-state scintillation devices, and poorly discriminate between the neutron and gamma rays. The boron nitride (BN)-CsPbBr₃ perovskite nanocomposite aerogel scintillator enables discriminative detection of thermal neutrons, features the largest known size (9 cm across), the lowest density (0.17 g cm^-3 ) among the existing scintillation materials, high BN (50%) perovskite (1%) contents, high optical transparency (85%), and excellent radiation stability. The new detection mechanism relies on thermal neutron capture by ¹⁰ B and effective energy transfer from the charged particles to visible-range scintillation photons between the densely packed BN and CsPbBr₃ nanocrystals. Low density minimizes the gamma ray response. The neutrons and gamma rays are discriminated by complete decoupling of the respective single pulses in time and intensity. These outcomes open new avenues for neutron detection in resource exploration, clean energy, environmental, aerospace, and homeland security applications.

Zero-dimensional Cu(I)-based organometallic halide with green cluster-centred emission for high resolution X-ray imaging screens

In this communication, we report a low-dimensional perovskite-related structure based on Cu(I) organometallic halide with strong green cluster-centred emission and near-unity photoluminescence quantum yield. The 0D [Rb(18-crown-6)]₂Cu₄I₆ was sucessfully applied for X-ray imaging screens which exhibit high spatial resolution of 16.8 lp mm^-1 and low detection limit of 458 nGy s^-1.

Hybrid Organic-Inorganic Perovskite Superstructures for Ultrapure Green Emissions

All inorganic CsPbBr₃ superstructures (SSs) have attracted much research interest due to their unique photophysical properties, such as their large emission red-shifts and super-radiant burst emissions. These properties are of particular interest in displays, lasers and photodetectors. Currently, the best-performing perovskite optoelectronic devices incorporate organic cations (methylammonium (MA), formamidinium (FA)), however, hybrid organic-inorganic perovskite SSs have not yet been investigated. This work is the first to report on the synthesis and photophysical characterization of APbBr₃ (A = MA, FA, Cs) perovskite SSs using a facile ligand-assisted reprecipitation method. At higher concentrations, the hybrid organic-inorganic MA/FAPbBr₃ nanocrystals self-assemble into SSs and produce red-shifted ultrapure green emissions, meeting the requirement of Rec. 2020 displays. We hope that this work will be seminal in advancing the exploration of perovskite SSs using mixed cation groups to further improve their optoelectronic applications.

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.

Color-Tunable and Stable Copper Iodide Cluster Scintillators for Efficient X-Ray Imaging

The search for color-tunable, efficient, and robust scintillators plays a vital role in the development of modern X-ray radiography. The radioluminescence tuning of copper iodide cluster scintillators in the entire visible region by bandgap engineering is herein reported. The bandgap engineering benefits from the fact that the conduction band minimum and valence band maximum of copper iodide cluster crystals are contributed by atomic orbitals from the inorganic core and organic ligand components, respectively. In addition to high scintillation performance, the as-prepared crystalline copper iodide cluster solids exhibit remarkable resistance toward both moisture and X-ray irradiation. These features allow copper iodide cluster scintillators to show particular attractiveness for low-dose X-ray radiography with a detection limit of 55  nGy s^-1 , a value ≈100 times lower than a standard dosage for X-ray examinations. The results suggest that optimizing both inorganic core and organic ligand for the building blocks of metal halide cluster crystals may provide new opportunities for a new generation of high-performance scintillation materials.

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.

Strain-Negligible Eu2+ Doping Enabled Color-Tunable Harsh Condition-Resistant Perovskite Nanocrystals for Superior Light-Emitting Diodes

Cesium lead halide (CsPbX₃, X = Br, Cl, I) perovskite nanocrystals (NCs) possess tunable band gaps across the entire visible spectral range and are promising for various optoelectronic device applications. However, poor performance in adverse conditions limits their further development in practical optoelectronics. Herein, highly stable perovskite NCs are developed by doping europium(II) (Eu²⁺) into the B-site of CsPbBr₃ with negligible lattice distortion/strain. Eu²⁺-doped CsPbBr₃ NCs exhibit tunable green-to-cyan emissions, high photoluminescence quantum yield, and good resistance to harsh conditions, including ultraviolet irradiation, erosion of moisture, and corrosion of polar solvent molecules. In particular, the thermal stability of CsPbBr₃ NCs after Eu²⁺ doping is greatly enhanced under continuous heating in air, while exhibiting the emissions of Eu²⁺. Furthermore, a Eu²⁺-doped CsPbBr₃ NC-based cyan light-emitting diode is fabricated, which exhibits narrow exciton emission driven under different current densities. This work would open the avenue to develop the rational lanthanide ion doping strategy for further advancing perovskite nanomaterials toward practical applications.

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.

Atomically flat semiconductor nanoplatelets for light-emitting applications

The last decade has witnessed extensive breakthroughs and significant progress in atomically flat two-dimensional (2D) semiconductor nanoplatelets (NPLs) in terms of synthesis, growth mechanisms, optical and electronic properties and practical applications. Such NPLs have electronic structures similar to those of quantum wells in which excitons are predominantly confined along the vertical direction, while electrons are free to move in the lateral directions, resulting in unique optical properties, such as extremely narrow emission line width, short photoluminescence (PL) lifetime, high gain coefficient, and giant oscillator strength transition (GOST). These unique optical properties make NPLs favorable for high color purity light-emitting applications, in particular in light-emitting diodes (LEDs), backlights for liquid crystal displays (LCDs) and lasers. This review article first introduces the intrinsic characteristics of 2D semiconductor NPLs with atomic flatness. Subsequently, the approaches and mechanisms for the controlled synthesis of atomically flat NPLs are summarized followed by an insight on recent progress in the mediation of core/shell, core/crown and core/crown@shell structures by selective epitaxial growth of passivation layers on different planes of NPLs. Moreover, an overview of the unique optical properties and the associated light-emitting applications is elaborated. Despite great progress in this research field, there are some issues relating to heavy metal elements such as Cd²⁺ in NPLs, and the ambiguous gain mechanisms of NPLs and others are the main obstacles that prevent NPLs from widespread applications. Therefore, a perspective is included at the end of this review article, in which the current challenges in this stimulating research field are discussed and possible solutions to tackle these challenges are proposed.

Advancing X-ray Luminescence for Imaging, Biosensing, and Theragnostics

X-ray luminescence is an optical phenomenon in which chemical compounds known as scintillators can emit short-wavelength light upon the excitation of X-ray photons. Since X-rays exhibit well-recognized advantages of deep penetration toward tissues and a minimal autofluorescence background in biological samples, X-ray luminescence has been increasingly becoming a promising optical tool for tackling the challenges in the fields of imaging, biosensing, and theragnostics. In recent years, the emergence of nanocrystal scintillators have further expanded the application scenarios of X-ray luminescence, such as high-resolution X-ray imaging, autofluorescence-free detection of biomarkers, and noninvasive phototherapy in deep tissues. Meanwhile, X-ray luminescence holds great promise in breaking the depth dependency of deep-seated lesion treatment and achieving synergistic radiotherapy with phototherapy.In this Account, we provide an overview of recent advances in developing advanced X-ray luminescence for applications in imaging, biosensing, theragnostics, and optogenetics neuromodulation. We first introduce solution-processed lead halide all-inorganic perovskite nanocrystal scintillators that are able to convert X-ray photons to multicolor X-ray luminescence. We have developed a perovskite nanoscintillator-based X-ray detector for high-resolution X-ray imaging of the internal structure of electronic circuits and biological samples. We further advanced the development of flexible X-ray luminescence imaging using solution-processable lanthanide-doped nanoscintillators featuring long-lived X-ray luminescence to image three-dimensional irregularly shaped objects. We also outline the general principles of high-contrast in vivo X-ray luminescence imaging which combines nanoscintillators with functional biomolecules such as aptamers, peptides, and antibodies. High-quality X-ray luminescence nanoprobes were engineered to achieve the high-sensitivity detection of various biomarkers, which enabled the avoidance of interference from the biological matrix autofluorescence and photon scattering. By marrying X-ray luminescence probes with stimuli-responsive materials, multifunctional theragnostic nanosystems were constructed for on-demand synergistic gas radiotherapy with excellent therapeutic effects. By taking advantage of the capability of X-rays to penetrate the skull, we also demonstrated the development of controllable, wireless optogenetic neuromodulation using X-ray luminescence probes while obviating damage from traditional optical fibers. Furthermore, we discussed in detail some challenges and future development of X-ray luminescence in terms of scintillator synthesis and surface modification, mechanism studies, and their other potential applications to provide useful guidance for further advancing the development of X-ray luminescence.

Highly luminescent dual-phase CsPbBr3/Cs4PbBr6 microcrystals for a wide color gamut for backlight displays

Cesium lead bromide perovskite nanocrystals (NCs) embedded in Cs₄PbBr₆ or CsPb₂Br₅ matrices forming core/shell structures are promising luminescent materials that exhibit remarkable photoluminescence properties meeting the need in a wide range of applications while overcoming stability challenges. Here, we report the large-scale, ligand-free synthesis of dual-phase Cs₄PbBr₆/CsPbBr₃ microcrystals (MCs) using ultrasonication at room temperature, exhibiting a high photoluminescence quantum yield (PLQY) of 82.7% and good stability. High-resolution transmission electron microscopy and X-ray photoelectron characterization confirm that CsPbBr₃ NCs are embedded in the Cs₄PbBr₆ matrix-forming CsPbBr₃/Cs₄PbBr₆ dual-phase structure. The evolution of the luminescence properties with temperature suggests that the strong green emission results from direct exciton recombination in the isolated [PbBr₆]^4- octahedra, which possess a large exciton binding energy of 283.6 meV. As revealed from their emission intensities, the dual-phase CsPbBr₃/Cs₄PbBr₆ MCs demonstrate excellent stability against ultraviolet irradiation (76%), good moisture resistance (42.7%), and good thermal tolerance (51%). It is understood that such excellent PLQY and stability are due to the surface passivation of the CsPbBr₃ NCs attributed to the large bandgap as well as the isolated [PbBr₆]^4- octahedra separated by Cs⁺ ions in the Cs₄PbBr₆ crystal lattice. Finally, the suitability of the green-emitting CsPbBr₃/Cs₄PbBr₆ material for achieving white-light emission and a wide color gamut is evaluated by constructing a prototype white light-emitting diode (w-LED) using CsPbBr₃/Cs₄PbBr₆ and red-emitting K₂SiF₆:Mn⁴⁺ materials taken in different weight ratios and combined with a blue light-emitting InGaN LED chip (λ = 455 nm). The constructed w-LED device exhibits the color coordinates (0.3315, 0.3289), an efficacy of 68 lm W^-1, a color rendering index of 87%, a color temperature of 5564 K, and a wide color gamut of ∼118.78% (NTSC) and ∼88.69% (Rec. 2020) with RGB color filters in the CIE 1931 color space. Therefore, based on our present findings, we strongly believe that the dual-phase CsPbBr₃/Cs₄PbBr₆ material is a promising green-emitting phosphor for use in w-LEDs as the backlight of display systems.

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.

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.

Recent progress and future prospects on halide perovskite nanocrystals for optoelectronics and beyond

As an emerging new class of semiconductor nanomaterials, halide perovskite (ABX₃, X = Cl, Br, or I) nanocrystals (NCs) are attracting increasing attention owing to their great potential in optoelectronics and beyond. This field has experienced rapid breakthroughs over the past few years. In this comprehensive review, halide perovskite NCs that are either freestanding or embedded in a matrix (e.g., perovskites, metal-organic frameworks, glass) will be discussed. We will summarize recent progress on the synthesis and post-synthesis methods of halide perovskite NCs. Characterizations of halide perovskite NCs by using a variety of techniques will be present. Tremendous efforts to tailor the optical and electronic properties of halide perovskite NCs in terms of manipulating their size, surface, and component will be highlighted. Physical insights gained on the unique optical and charge-carrier transport properties will be provided. Importantly, the growing potential of halide perovskite NCs for advancing optoelectronic applications and beyond including light-emitting devices (LEDs), solar cells, scintillators and X-ray imaging, lasers, thin-film transistors (TFTs), artificial synapses, and light communication will be extensively discussed, along with prospecting their development in the future.

Thermally Activated Delayed Fluorescence Zirconium-Based Perovskites for Large-Area and Ultraflexible X-ray Scintillator Screens

Flexible scintillator screens with environmental stability, high sensitivity, and low cost have emerged as candidates for X-ray imaging applications. Here, a large-scale and cost-efficient solution synthesis of the vacancy-ordered double perovskite Cs₂ ZrCl₆ , which is characterized by thermal activation delayed fluorescence (TADF) dominated by triplet emission under X-ray irradiation, is demonstrated. The large Stokes shift and efficient luminescence collection of TADF effectively ensure the light outcoupling efficiency. Further, flexible X-ray scintillator screens with an area of 400 cm² are prepared using poly(dimethylsiloxane) (PDMS) as the carrier, exhibiting excellent scintillation properties with light yields as high as 49 400 photons MeV^-1 , spatial resolutions up to 18 lp mm^-1 and detection limits as low as 65 nGy s^-1 . Finally, the high-quality imaging results of non-planar and dynamic objects by such screens are demonstrated. It is believed that the explored Cs₂ ZrCl₆ @PDMS flexible scintillator screens would offer a big step toward expanding the application range of scintillators in different environments.

Multispectral Large-Panel X-ray Imaging Enabled by Stacked Metal Halide Scintillators

Conventional energy-integration black-white X-ray imaging lacks the spectral information of X-ray photons. Although X-ray spectra (energy) can be distinguished by the photon-counting technique typically with CdZnTe detectors, it is very challenging to be applied to large-area flat-panel X-ray imaging (FPXI). Herein, multilayer stacked scintillators of different X-ray absorption capabilities and scintillation spectra are designed; in this scenario, the X-ray energy can be discriminated by detecting the emission spectra of each scintillator; therefore, multispectral X-ray imaging can be easily obtained by color or multispectral visible-light camera in a single shot of X-rays. To verify this idea, stacked multilayer scintillators based on several emerging metal halides are fabricated in a cost-effective and scalable solution process, and proof-of-concept multispectral (or multi-energy) FPXI are experimentally demonstrated. The dual-energy X-ray image of a "bone-muscle" model clearly shows the details that are invisible in conventional energy-integration FPXI. By stacking four layers of specifically designed multilayer scintillators with appropriate thicknesses, a prototype FPXI with four energy channels is realized, proving its extendibility to multispectral or even hyperspectral X-ray imaging. This study provides a facile and effective strategy to realize multispectral large-area flat-panel X-ray imaging.

Cryogenic Scintillation Properties of Lead-Free Cs3Cu2I5 Single Crystals

Perovskite scintillators have become increasingly popular in recent years because of their simple production and high sensitivity to X-ray. Due to large Stokes shifts, high light yield, eco-friendly fabrication, and good stability, the lead-free Cu-based perovskites have gained much attention. In this paper, we prepared the Cs₃Cu₂I₅ single crystals (SCs) by the solution-processed method. At room temperature, we measured the emission band at 440 nm with an average decay time of 595 ns under X-ray excitation. Under ¹³⁷Cs γ-ray excitation, we determined that the light yield of Cs₃Cu₂I₅ SCs was 23 000 photons/MeV. Notably, under alpha particle excitation by ²⁴¹Am, the light yield of Cs₃Cu₂I₅ SCs is approximately 3.2 times higher than that of the commercial scintillator LYSO(Ce). In addition, we systematically investigated the cryogenic scintillation properties of Cs₃Cu₂I₅ SCs at the temperature range of 60-300 K. With decreasing temperature, the intensity of the emission band at 440 nm significantly increases, and an additional emission band at 336 nm emerges below 100 K. Meanwhile, the temperature-dependent decay times were determined. The fast and slow decay time of Cs₃Cu₂I₅ SCs are estimated to be 221 and 1193 ns, respectively, at 60 K. Our findings highlight the great potential for Cs₃Cu₂I₅ SCs to be a cryogenic scintillator.

Anthracene Single-Crystal Scintillators for Computer Tomography Scanning

X-ray imaging and computed tomography (CT) technology, as the important non-destructive measurements, can observe internal structures without destroying the detected sample, which are always used in biological diagnosis to detect tumors, pathologies, and bone damages. It is always a challenge to find materials with a low detection limit, a short exposure time, and high resolution to reduce X-ray damage and acquire high-contrast images. Here, we described a low-cost and high-efficient method to prepare centimeter-sized anthracene crystals, which exhibited intense X-ray radioluminescence with a detection limit of ∼0.108 μGy s^-1, which is only one-fifth of the dose typically used for X-ray diagnostics. Additionally, the low absorption reduced the damage in radiation and ensured superior cycle performance. X-ray detectors based on anthracene crystals also exhibited an extremely high resolution of 40 lp mm^-1. The CT scanning and reconstruction of a foam sample were then achieved, and the detailed internal structure could be clearly observed. These indicated that organic crystals are expecting to be leading candidate low-cost materials for low-dose and highly sensitive X-ray detection and CT scanning.

Micrometer-Resolution X-ray Imaging Enabled by a Flexible Perovskite Screen

Spatial resolution improvement has been keenly sought recently in the perovskite-based scintillation community. Here, micrometer resolution (∼2.0 μm) was achieved by using an X-ray imaging screen of self-assembled perovskite nanosheets. The assembly behavior of nanosheets was applicable to many substrates, including glass, metal, and polymer surfaces. The use of a polymer substrate not only eliminated the parasite absorption of X-ray but also enabled a flexible screen with robust bending stability. The assembly behavior, on the other hand, provided vicinity for an efficient energy transfer between nanosheets of varied thicknesses, as evidenced by both transient absorption and photoluminescence lifetime measurements. Importantly, the ensuing large Stokes shift (∼316 meV) significantly mitigated the reabsorption issue, leading to a comparable light yield to LYSO/Ce crystals. With the aid of the synchrotron-based collimated X-ray beam, the fine structure of two-dimensional objects, such as microchips, was clearly visualized with the flexible scintillation screen. Furthermore, those challenging biological samples were also scanned by phase-contrast imaging, whereby a three-dimensional reconstruction was obtained successfully. Despite the labile nature of the perovskite screen, this work represents the state-of-the-art spatial resolution for perovskite scintillation.

Ag Nanocluster-Enhanced Scintillation Properties of Borophosphate Glasses Doped with CsPbBr3 Quantum Dots

A novel and effective method to improve scintillation properties of glass-ceramics, such as intensity enhancement and decay-time shortening, is reported in this work. Compared with crystal scintillators, glass scintillators always have the problems of low efficiency and long decay; how to solve them has always been a scientific puzzle in the field of scintillation glass-ceramics. The plasma enhancement effect can be predicted to solve the above problems. Ag⁺ ions were diffused into glasses by ion exchange, and then Ag nanoparticles and CsPbBr₃ quantum dots were formed by heat treatment. The structure of the CsPbBr₃ perovskite consists of a series of shared corner PbBr₆ octahedra with Cs ions occupying the cuboctahedral cavities. By using Ag and the plasma resonance effect, the photoluminescence intensity of CsPbBr₃ quantum dot glasses was enhanced by 3 times, its radioluminescence intensity increased by 6.25 times, and its decay time was reduced by a factor of more than one. Moreover, the mechanism of photoluminescence and radioluminescence enhanced by Ag and plasma was discussed based on the experimental results and finite-difference time-domain method. We concluded that the increase in radioluminescence intensity was related to plasma enhancements and the energy exchange between Ag nanoclusters and CsPbBr₃ quantum dots. Doping Ag is a valid means to improve the scintillation luminescence of CsPbBr₃ quantum dot glasses, which can be applied in the field of scintillation.