Double Perovskite Single Crystals with High Laser Irradiation Stability for Solid-State Laser Lighting and Anti-counterfeiting

Laser lighting devices, comprising an ultraviolet (UV) laser chip and a phosphor material, have emerged as a highly efficient approach for generating high-brightness light sources. However, the high power density of laser excitation may exacerbate thermal quenching in conventional polycrystalline or amorphous phosphors, leading to luminous saturation and the eventual failure of the device. Here, for the first time, we raise a single-crystal (SCs) material for laser lighting considering the absence of grain boundaries that scatter electrons and phonons, achieving high thermal conductivity (0.81 W m-1 K-1) and heat-resistance (575 °C). The SCs products exhibit a high photoluminescence quantum yield (89%) as well as excellent stability toward high-power lasers (>12.41 kW/cm2), superior to all previously reported amorphous or polycrystalline matrices. Finally, the laser lighting device was fabricated by assembling the SC with a UV laser chip (50 mW), and the device can maintain its performance even after continuous operation for 4 h. Double perovskite single crystals doped with Yb3+/Er3+ demonstrated multimodal luminescence with the irradiation of 355 and 980 nm lasers, respectively. This characteristic holds significant promise for applications in spectrally tunable laser lighting and multimodal anticounterfeiting.

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

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

Reconfigurable perovskite X-ray detector for intelligent imaging

X-ray detection is widely used in various applications. However, to meet the demand for high image quality and high accuracy diagnosis, the raw data increases and imposes challenges for conventional X-ray detection hardware regarding data transmission and power consumption. To tackle these issues, we present a scheme of in-X-ray-detector computing based on CsPbBr3 single-crystal detector with convenient polarity reconfigurability, good linear dynamic range, and robust stability. The detector features a stable trap-free device structure and achieves a high linear dynamic range of 106 dB. As a result, the detector could achieve edge extraction imaging with a data compression ratio of ~50%, and could also be programmed and trained to perform pattern recognition tasks with a high accuracy of 100%. Our research shows that in-X-ray-detector computing can be used in flexible and complex scenarios, making it a promising platform for intelligent X-ray imaging.

Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings

BACKGROUND

Translucent monolithic zirconia ceramics have been applied in dental clinics due to their esthetic translucent formulations and mechanical properties. Considering inherent ceramic brittleness, adhesive bonding with resin composite increases the fracture resistance of ceramic restorations. However, zirconia is a chemically stable material that is difficult to adhesively bond with resin.

OBJECTIVES

To investigate the influences of SiO2-ZrO2 coatings on adhesive bonding of zirconia and the surface characterization of those coatings.

METHODS AND MATERIALS

Translucent zirconia discs were classified into groups based on surface treatments: CT (control), SB (sandblasting), C21(SiO2:ZrO2=2:1), C11(SiO2:ZrO2=1:1), and C12 (SiO2:ZrO2=1:2) (n=10). Surface characterization of coatings on zirconia were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), surface roughness assessment (Ra), X-ray diffraction (XRD), water contact angle (WCA), translucency parameter (TP), and shear bond strength (SBS). Two-way ANOVA for shear bond strength results and ANOVA for Ra and WCA were performed.

RESULTS

SEM images revealed SiO2 islands on zirconia disks coated with SiO2-ZrO2. Surface roughness of C12, C11, and C21 groups was significantly larger than those of groups SB and CT (p<0.05). XRD results showed that phase transformation of zirconia disks was detected only in the SB group. In addition, SiO2-ZrO2 coatings reduced WCA. The translucency decreased only in group C21. Group C11 showed the highest shear bond strength under both aging conditions.

CONCLUSION

SiO2-ZrO2 coating is a promising method to enhance the adhesive resin bonding of translucent zirconia without causing phase transformation of translucent zirconia.

Rheological engineering of perovskite suspension toward high-resolution X-ray flat-panel detector

Solution-processed polycrystalline perovskite film is promising for the next generation X-ray imaging. However, the spatial resolution of current perovskite X-ray panel detectors is far lower than the theoretical limit. Herein we find that the pixel level non-uniformity, also known as fixed pattern noise, is the chief culprit affecting the signal-to-noise ratio and reducing the resolution of perovskite detectors. We report a synergistic strategy of rheological engineering the perovskite suspensions to achieve X-ray flat panel detectors with pixel-level high uniformity and near-to-limit spatial resolution. Our approach includes the addition of methylammonium iodide and polyacrylonitrile to the perovskite suspension, to synergistically enhance the flowability and particle stability of the oversaturated solution. The obtained suspension perfectly suits for the blade-coating process, avoiding the uneven distribution of solutes and particles within perovskite films. The assembled perovskite panel detector exhibits greatly improved fixed pattern noise value (1.39%), high sensitivity (2.24 × 104 μC Gyair-1 cm-2), low detection limit (28.57 nGyair·s-1) as well as good working stability, close to the performance of single crystal detectors. Moreover, the detector achieves a near-to-limit resolution of 0.51 lp/pix.

Direct Fast-Neutron Detection by 2D Perovskite Semiconductor

Fast-neutrons play a critical role in a range of applications, including medical imaging, therapy, and nondestructive inspection. However, direct detecting fast-neutrons by semiconductors has proven to be challenging due to their weak interaction with most matter and the requirement of high carrier mobility-lifetime (µτ) product for efficient charge collection. Herein, a novel approach is presented to direct fast-neutron detection using 2D Dion-Jacobson perovskite semiconductor BDAPbBr4 . This material features a high fast-neutron caption cross-section, good electrical stability, high resistivity, and, most importantly, a record-high µτ product of 3.3 × 10-4 cm2 V-1 , outperforming most reported fast-neutron detection semiconductors. As a result, BDAPbBr4 detector exhibited good response to fast-neutrons, not only achieving fast-neutron energy spectra in counting mode, but also obtaining linear and fast response in integration mode. This work provides a paradigm-shifting strategy for designing materials that efficiently detect fast-neutrons and paves the way toward exciting applications in fast-neutron imaging and therapy.

Learning Intention-Aware Policies in Deep Reinforcement Learning

Deep reinforcement learning (DRL) provides an agent with an optimal policy so as to maximize the cumulative rewards. The policy defined in DRL mainly depends on the state, historical memory, and policy model parameters. However, we humans usually take actions according to our own intentions, such as moving fast or slow, besides the elements included in the traditional policy models. In order to make the action-choosing mechanism more similar to humans and make the agent to select actions that incorporate intentions, we propose an intention-aware policy learning method in this letter To formalize this process, we first define an intention-aware policy by incorporating the intention information into the policy model, which is learned by maximizing the cumulative rewards with the mutual information (MI) between the intention and the action. Then we derive an approximation of the MI objective that can be optimized efficiently. Finally, we demonstrate the effectiveness of the intention-aware policy in the classical MuJoCo control task and the multigoal continuous chain walking task.

Flexible and broadband colloidal quantum dots photodiode array for pixel-level X-ray to near-infrared image fusion

Combining information from multispectral images into a fused image is informative and beneficial for human or machine perception. Currently, multiple photodetectors with different response bands are used, which require complicated algorithms and systems to solve the pixel and position mismatch problem. An ideal solution would be pixel-level multispectral image fusion, which involves multispectral image using the same photodetector and circumventing the mismatch problem. Here we presented the potential of pixel-level multispectral image fusion utilizing colloidal quantum dots photodiode array, with a broadband response range from X-ray to near infrared and excellent tolerance for bending and X-ray irradiation. The colloidal quantum dots photodiode array showed a specific detectivity exceeding 1012 Jones in visible and near infrared range and a favorable volume sensitivity of approximately 2 × 105 μC Gy-1 cm-3 for X-ray irradiation. To showcase the advantages of pixel-level multispectral image fusion, we imaged a capsule enfolding an iron wire and soft plastic, successfully revealing internal information through an X-ray to near infrared fused image.

One-dimensional scintillator film with benign grain boundaries for high-resolution and fast x-ray imaging

Fast and high-resolution x-ray imaging demands scintillator films with negligible afterglow, high scintillation yield, and minimized cross-talk. However, grain boundaries (GBs) are abundant in polycrystalline scintillator film, and, for current inorganic scintillators, detrimental dangling bonds at GBs inevitably extend radioluminescence lifetime and increase nonradiative recombination loss, deteriorating afterglow and scintillation yield. Here, we demonstrate that scintillators with one-dimensional (1D) crystal structure, Cs₅Cu₃Cl₆I₂ explored here, possess benign GBs without dangling bonds, yielding nearly identical afterglow and scintillation yield for single crystals and polycrystalline films. Because of its 1D crystal structure, Cs₅Cu₃Cl₆I₂ films with desired columnar morphology are easily obtained via close space sublimation, exhibit negligible afterglow (0.1% at 10 ms) and high scintillation yield (1.2 times of CsI:Tl). We have also demonstrated fast x-ray imaging with 27 line pairs mm^-1 resolution and frame rate up to 33 fps, surpassing most existing scintillators. We believe that the 1D scintillators can greatly boost x-ray imaging performance.

Advances in the Application of Perovskite Materials

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

Growth mechanism of metal halide perovskite single crystals in solution

Metal halide perovskite (MHP) single crystals (SCs) have been demonstrated to have significant potential in photodetectors and photovoltaic devices due to their exceptional optoelectronic properties. The most promising approach for large-scale fabrication of high-quality MHP SCs is the synthesis of MHP SCs in solution. To explain the mechanism and guide the crystal growth process, the classical nucleation-growth theory was established. However, it mainly focuses on zone melting systems and does not account for the interaction between perovskite and solvent. In this review, we specifically focus on the difference in the growth mechanism between MHP SCs in solution and traditional SCs synthesized by the melting method, which includes a discussion of the dissolution, nucleation, and growth processes. We then summarize recent advances in the preparation of MHP SCs based on the special growth mechanism of the perovskite system. The purpose of this review is to provide comprehensive information to offer targeted theoretical guidance as well as unified understanding for the preparation of high-quality MHP SCs in solution.

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).

Mechanochemical Synthesis of High-Entropy Perovskite toward Highly Sensitive and Stable X-ray Flat-Panel Detectors

Perovskites are attracting attention for optoelectronic devices. Despite their promise, the large-scale synthesis of perovskite materials with exact stoichiometry, especially high-entropy perovskites, has been a major challenge. Moreover, the difficulty in stoichiometry control also hinders the development of perovskite X-ray flat-panel detectors. Previous reports all employed simple MAPbI₃ as the active layer, while the performance still falls short of optimized single-crystal-based single-pixel detectors. Herein, a scalable and universal strategy of a mechanochemical method is adopted to synthesize stoichiometric high-entropy perovskite powders with high quality and high quantity (>1 kg per batch). By utilizing these stoichiometric perovskites, the first FA_0.9 MA_0.05 Cs_0.05 Pb(I_0.9 Br_0.1 )₃ -based X-ray flat-panel detector with low trap density and large mobility-lifetime product (7.5 × 10^-3 cm² V^-1 ) is reported. The assembled panel detector exhibits close-to-single-crystal performance (high sensitivity of 2.1 × 10⁴ µC Gy_air ^-1 cm^-2 and ultralow detection limit of 1.25 nGy_air s^-1 ), high spatial resolution of 0.46 lp/pixel, as well as excellent thermal robustness under industrial standards. The high performance in the high-entropy perovskite-based X-ray FPDs has the potential to facilitate the development of new-generation X-ray-detection systems.

Dark current modeling of thick perovskite X-ray detectors

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

Continuous and Scalable Production of Platinum Nanocubes with Uniform and Controllable Sizes in Air-Free Droplet Reactors

Platinum (Pt) nanocrystals hold the key to a variety of catalytic applications, and those with a cubic shape are attractive as a reference catalyst due to their well-defined {100} facets on the surface. Here we demonstrate the use of droplet reactors as a viable platform for the continuous and scalable production of Pt nanocubes with uniform and controllable sizes. The synthesis was found to be sensitive to the O₂ from air because of the oxidative etching associated with the O₂/Br^- pair. As such, either silicone oil or an inert gas had to be employed as the carrier phase to keep the droplets isolated from air. By controlling the amounts of the precursor and halide ions, the edge length of the Pt nanocubes could be tuned from 5-7 nm. In the setting of a millifluidic device, the droplet reactors could be used to achieve a production rate as high as 31.8 mg min^-1, about 10-100 times greater than what has been reported in the literature. We also evaluated the electrocatalytic properties of the as-obtained Pt nanocubes toward the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). For the Pt nanocubes of 6 nm in edge length, they showed a specific activity of 0.27 mA cm^-2 toward ORR at 0.9 V and a specific activity of 0.96 mA cm^-2 toward MOR at the anodic potential.

Vertical matrix perovskite X-ray detector for effective multi-energy discrimination

Multi-energy X-ray detection is sought after for a wide range of applications including medical imaging, security checking and industrial flaw inspection. Perovskite X-ray detectors are superior in terms of high sensitivity and low detection limit, which lays a foundation for multi-energy discrimination. However, the extended capability of the perovskite detector for multi-energy X-ray detection is challenging and has never been reported. Herein we report the design of vertical matrix perovskite X-ray detectors for multi-energy detection, based on the attenuation behavior of X-ray within the detector and machine learning algorithm. This platform is independent of the complex X-ray source components that constrain the energy discrimination capability. We show that the incident X-ray spectra could be accurately reconstructed from the conversion matrix and measured photocurrent response. Moreover, the detector could produce a set of images containing the density-graded information under single exposure, and locate the concealed position for all low-, medium- and high-density substances. Our findings suggest a new generation of X-ray detectors with features of multi-energy discrimination, density differentiation, and contrast-enhanced imaging.

Chemical Potential Diagram Guided Rational Tuning of Electrical Properties: A Case Study of CsPbBr3 for X-ray Detection

Controlling the carrier polarity and concentration underlies most electronic and optoelectronic devices. However, for the intensively studied lead halide perovskites, the doping tunability is inefficient. In this work, taking CsPbBr₃ as an example, it is revealed that the coexistence of metallic Pb or CsBr₃ /Br₂ , rather than the precursor ratio, can provide Pb-rich/Br-poor or Br-rich/Pb-poor chemical conditions, enabling the tunability of electrical properties from weak n-type, intrinsic, to moderate p-type. Experimentally, under Br₂ -exposure treatment, a shift of the Fermi level as large as 1.00 eV is achieved, which is one of the highest value among all kinds of doping methods. The X-ray detector based on the intrinsic CsPbBr₃ exhibits excellent performance, with a negligible dark-current drift of 7.1 × 10^-4 nA cm^-1 s^-1 V^-1 , a low detection limit of 103.6 nGy_air s^-1 , and a high sensitivity of 9085 μC Gy_air ^-1 cm^-2 . This work provides a critical understanding and guidance for tuning the electrical properties of lead halide perovskites, which establishes good foundations for achieving intrinsic perovskite semiconductors and also constructing potential homojunction devices.

Lead-Free Zero-Dimensional Organic-Copper(I) Halides as Stable and Sensitive X-ray Scintillators

Low-dimensional organic-metal halides are regarded as an emerging class of X-ray scintillation materials, but most of the discovered compounds are confronted with challenges of toxicity and instability. To address these challenges, we herein report two lead-free zero-dimensional (0D) hybrid halides, (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ single crystals, grown by the low-cost solution-processing method. By single-crystal X-ray diffraction refinement, the crystal structures of (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ were determined to be orthorhombic and monoclinic crystal systems, respectively. (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ show broadband orange and yellow emissions peaking at 620 and 538 nm, respectively. Different from the emission nature of the recent reported Cu-based halide hybrids, both (Bmpip)₂Cu₂Br₄ and PPh₄CuBr₂ emit from excitons bound to defects featuring spin-allowed transition, enabling them to possess fast scintillation decay time of tens of nanoseconds, respectively. In particular, the (Bmpip)₂Cu₂Br₄ single crystal has a high photoluminescence quantum yield of 48.2%, a high scintillation yield of 16,000 photons/MeV, and a low detection limit of 710 nGy_air/s. Due to the combination of nontoxicity, long-term stability, and decent detection performance, (Bmpip)₂Cu₂Br₄ could be regarded as a promising X-ray scintillator.

Formamidinium Perovskitizers and Aromatic Spacers Synergistically Building Bilayer Dion-Jacobson Perovskite Photoelectric Bulk Crystals

Two-dimensional (2D) multilayer Dion-Jacobson (DJ) phase organic inorganic hybrid perovskites (OIHPs) have attracted extensive research attention due to the high stability and excellent charge-transport properties in the optoelectronic field. However, the synthesis of 2D multilayer DJ OIHPs is still very challenging. Until now, only few multilayer DJ perovskites have been reported and most of them are based on volatile methylamine (MA) cations. Compared with MA-based OIHPs, the OIHPs constructed with formamidinium (FA) as perovskitizers not only improve the stability but also extend the light absorption range. Meanwhile, the introducing aromatic diamines as spacers could promote the electron-hole separation in such DJ hybrids. However, the DJ OIHP bulk single crystal constructed by using the advantages of FA as perovskitizers and aromatic diamines as spacers is still blank. Herein, we integrate the properties of organic cations and inorganic skeletons at a molecular-scale to construct a broadband-responsive 2D bilayer DJ perovskite (3AMPY)(FA)Pb₂I₇ [3AMPY = 3-(aminomethyl)pyridinium], which shows a fascinating detectivity from X-ray (5.23 × 10⁴ μC Gy_air^-1 cm^-2 at 200 V bias) and visible light (6 × 10¹² jones at 637 nm) to the near-infrared region (2.6 × 10⁹ jones at 780 nm). After an in-depth analysis of structure and optical properties, we found that the distortion degree of Pb-I-Pb bond angles between adjacent PbI₆ octahedra plays a crucial role on optical properties; on the other hand, the interlayer spacer cations (3AMPY) and intralayer perovskitizers (FA) mutual participate in the contribution of the conduction band, making (3AMPY)(FA)Pb₂I₇ have a narrow optical band gap of 1.54 eV. Such a 2D perovskite material with a wide spectra response will be the preferred choice for photodetection under complex conditions.

A Hierarchical Bayesian Latent Class Model for the Diagnostic Performance of Mini-Mental State Examination and Montreal Cognitive Assessment in Screening Mild Cognitive Impairment Due to Alzheimer's Disease

BACKGROUND

The Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) are low costing and noninvasive neuropsychological tests in screening Mild Cognitive Impairment (MCI) due to Alzheimer's disease (AD). There is no consensus on which test performs better in detecting MCI due to AD based on the different imperfect reference standards. Therefore, we conducted a meta-analysis to assess the diagnostic performance of MMSE and MoCA for screening MCI due to AD in the absence of a gold standard.

METHODS

Six electronic databases were searched for relevant studies until April, 2022. A hierarchical Bayesian latent class model was used to estimate the pooled sensitivity and specificity of MoCA and MMSE in the absence of a gold standard.

RESULTS

90 eligible studies covering 21273 individuals for MMSE, 26631 individuals for MoCA were included in this meta-analysis. The pooled sensitivity was 0.71(95%CI: 0.67-0.74) for MMSE and 0.85(95%CI: 0.83-0.88) for MoCA, while the pooled specificity was 0.71(95%CI: 0.68-0.74) for MMSE and 0.79(95%CI: 0.76-0.81) for MoCA. MoCA was useful to "rule in" and "rule out" the diagnosis of MCI due to AD with higher positive likelihood ratio (4.07; 95%CI: 3.60-4.62) and lower negative likelihood ratio (0.18; 95%CI: 0.16-0.22). Moreover, the diagnostic odds ratio of MoCA was 22.08(95%CI: 17.24-28.29), which showed significantly favorable diagnostic performance.

CONCLUSIONS

It suggests that MoCA has greater diagnostic performance than MMSE for differentiating MCI due to AD when the gold standard is absent. However, these results should be taken with caution given the heterogeneity observed.

Decreasing Structural Dimensionality of Double Perovskites for Phase Stabilization toward Efficient X-ray Detection

Halide double perovskites have attracted substantial attention for optoelectronic applications owing to their low toxicity and high stability. However, double perovskites have strict requirements in terms of the halide type, thus rendering many of their properties unchangeable, including the band gap, atomic number, and carrier transport. By introducing long-chain organic amines, the chloride site of double perovskites can be completely replaced by bromide. Using this strategy, two dimensions silver-indium-bromide double perovskites (PEA)₄AgInBr₈ and (i-BA)₄AgInBr₈ were successfully synthesized [(PEA)⁺ = C₆H₅(CH₂)₂NH₃⁺, (i-BA)⁺ = CH(CH₃)₂CH₂NH₃⁺]. Density functional theory calculations and spectroscopy characterizations were performed to unveil the semiconducting behaviors and photoluminescence properties of the title compounds. Electrical characterization confirms their good carrier-transport property (μτ product: 2.0 × 10^-3 cm² V^-1) and low dark current. Moreover, the presence of heavy atoms, together with the ultrastable baseline contributes to a high X-ray detection sensitivity (185 μC Gy_air^-1 cm^-2), greater than that of most previous double-perovskite detectors. Our work lays the foundation for broadening the family of potential double perovskites, creating a new path for the realization of long-sought perovskites with low toxicity and high stability that retain good optoelectronic performance.

Oxide perovskite Ba2AgIO6 wafers for X-ray detection

X-ray detection is of great significance in biomedical, nondestructive, and scientific research. Lead halide perovskites have recently emerged as one of the most promising materials for direct X-ray detection. However, the lead toxicity remains a worrisome concern for further commercial application. Great efforts have been made to search for lead-free perovskites with similar optoelectronic properties. Here, we present a lead-free oxide double perovskite material Ba₂AgIO₆ for X-ray detection. The lead-free, all-inorganic nature, as well as the high density of Ba₂AgIO₆, promises excellent prospects in X-ray applications. By employing the hydrothermal method, we successfully synthesized highly crystalline Ba₂AgIO₆ powder with pure phase. Furthermore, we prepared Ba₂AgIO₆ wafers through isostatic pressure and built X-ray detectors with Au/Ba₂AgIO₆ wafer/Au photo-conductive structure. The as-prepared X-ray detectors showed a sensitivity of 18.9 µC/(Gy_air·cm²) at 5 V/mm, similar to commercial α-Se detectors showcasing their advantages for X-ray detection.

Efficient Blue Light Emitting Diodes Based On Europium Halide Perovskites

Flat panel displays enjoy 100 billion-dollar markets with significant penetration in daily life, which require efficient, color-saturated blue, green, and red light-emitting diodes (LEDs). The recently emerged halide perovskites have demonstrated low-cost and outstanding performance for potential LED applications. However, the performance of blue perovskite LEDs (PeLEDs) lags far behind red and green cousins, particularly for color coordinates approaching (0.131, 0.046) that fulfill the Rec. 2020 specification for blue emitters. Here, a high-efficiency, lead-free perovskite, CsEuBr₃ , is reported that exhibits bright blue exciton emission centered at 448 nm with a color coordinates of (0.15, 0.04), contributed from Eu-5d→Eu-4f/Br-4p transition with an optical band gap of 2.85 eV. Further optical characterizations reveal its short excited-state lifetime of 151 ns, excellent exciton diffusion diffusivity of 0.0227 cm² s^-1 , and high quantum yield of ≈69%. Inspired by these findings, deep-blue PeLEDs based on all-vacuum processing methods, which have been demonstrated as the most successful approach for the organic LED industry, are constructed. The devices show a maximum external quantum efficiency of 6.5% with an operating half-lifetime of 50 mins at an initial brightness of 15.9 cd m^-2 . It is anticipated that this work will inspire further research on lanthanide-based perovskites for next-generation LED applications.

Sb2Se3 film with grain size over 10 µm toward X-ray detection

Direct X-ray detectors are considered as competitive next-generation X-ray detectors because of their high spatial resolution, high sensitivity, and simple device configuration. However, their potential is largely limited by the imperfections of traditional materials, such as the low crystallization temperature of α-Se and the low atomic numbers of α-Si and α-Se. Here, we report the Sb₂Se₃ X-ray thin-film detector with a p-n junction structure, which exhibited a sensitivity of 106.3 µC/(Gy_air·cm²) and response time of < 2.5 ms. This decent performance and the various advantages of Sb₂Se₃, such as the average atomic number of 40.8 and μτ product (μ is the mobility, and τ is the carrier lifetime) of 1.29 × 10^-5 cm²/V, indicate its potential for application in X-ray detection.

Highly Luminescent Zero-Dimensional Organic Copper Halides for X-ray Scintillation

The present work reports highly efficient flexible and reabsorption-free scintillators based on two zero-dimensional (0D) organic copper halides (TBA)CuX₂ (TBA = tetrabutylammonium cation; X = Cl, Br). The (TBA)CuX₂ exhibit highly luminescent green and sky-blue emissions peaked at 510 and 498 nm, with large Stokes shifts of 224 and 209 nm and high photoluminescence quantum yields (PLQYs) of 92.8% and 80.5% at room temperature for (TBA)CuCl₂ and (TBA)CuBr₂ single crystals (SCs), respectively. Interestingly, above room temperature, their PLQYs increase with temperature and reach near unity at 320 and 345 K for (TBA)CuCl₂ and (TBA)CuBr₂, respectively. The excellent properties originate from self-trapped excitons (STEs) in individual [CuX₂]^- quantum rods, which is demonstrated by the temperature-dependent PL, ultrafast transient absorption (TA) combined with density functional theory (DFT) calculations. The (TBA)CuX₂ scintillators show bright radioluminescence (RL), impressive linear response to dose rate in a broad range, and high light yields. Their potential application in X-ray imaging is demonstrated by using (TBA)CuX₂ composite scintillation screens. Importantly, flexible scintillators are demonstrated to be superior than flat ones for imaging nonplanar objects by conformally coating, which produce accurate images with negligible distortion.

Lead halide perovskite for efficient optoacoustic conversion and application toward high-resolution ultrasound imaging

Lead halide perovskites have exhibited excellent performance in solar cells, LEDs and detectors. Thermal properties of perovskites, such as heat capacity and thermal conductivity, have rarely been studied and corresponding devices have barely been explored. Considering the high absorption coefficient (104~105 cm-1), low specific heat capacity (296-326 J kg-1 K-1) and small thermal diffusion coefficient (0.145 mm2 s-1), herein we showcase the successful use of perovskite in optoacoustic transducers. The theoretically calculated phonon spectrum shows that the overlap of optical phonons and acoustic phonons leads to the up-conversion of acoustic phonons, and thus results in experimentally measured low thermal diffusion coefficient. The assembled device of PDMS/MAPbI3/PDMS simultaneously achieves broad bandwidths (-6 dB bandwidth: 40.8 MHz; central frequency: 29.2 MHz), and high conversion efficiency (2.97 × 10-2), while all these parameters are the record values for optoacoustic transducers. We also fabricate miniatured devices by assembling perovskite film onto fibers, and clearly resolve the fine structure of fisheyes, which demonstrates the strong competitiveness of perovskite based optoacoustic transducers for ultrasound imaging.

Efficient Dual-Band White-Light Emission with High Color Rendering from Zero-Dimensional Organic Copper Iodide

Broad-band white-light emissions from organic-inorganic lead halide hybrids have attracted considerable attention in energy-saving solid-state lighting (SSL) applications. However, the toxicity of lead in these hybrids hinders their commercial prospects, and the low photoluminescence quantum yields (PLQYs) cannot meet the requirements for efficient lighting. Here, we report a highly efficient dual-band white-light emission from organic copper iodide, (C₁₆H₃₆N)CuI₂, which exhibits a high PLQY of 54.3% and excellent air stability. The single-crystalline (C₁₆H₃₆N)CuI₂ possesses a unique zero-dimensional (0D) structure, in which the isolated [Cu₂I₄]^2- dimers are periodically embedded in the wide band gap organic framework of C₁₆H₃₆N⁺. This perfect 0D structure can cause significant quantum confinement and strong electron-phonon coupling, which contributes to efficient emissions from self-trapped excitons (STEs). Photophysical studies revealed the presence of two self-trapped emitting states in [Cu₂I₄]^2- dimers, whose populations are highly sensitive to the temperature that governs the molecular environment for [Cu₂I₄]^2- dimers and the thermal activation energy of STEs. An ultraviolet (UV) excited white light-emitting diode fabricated using this single-phase white-light emitter exhibits a high color rendering index (CRI) of 78. The new material provides a promising emitter, having a high PLQY and a high CRI simultaneously, for SSL and display applications.

Characterizing the air pollution of the cities in the closure of corona virus disease 2019 in China

With the rapid development of industrialization and urbanization in China, energy and vehicle consumption have continued to increase in recent years and air pollution has become serious. In early 2020, Corona Virus Disease 2019 broke out in Wuhan, China. From January 29, 2020, several sources of the air pollution almost all stopped working, including gasoline burning vehicles, dust producing building sites, coal-fired factories, etc. Five indicators of the atmospheric environmental quality were observed from December 19, 2019 to April 30, 2020 in nine cities and 1-h average concentrations, 24-h average concentrations and Air Quality Index were assessed. The 1-h average concentrations of the nitrogen dioxide, the ozone and the sulfur dioxide showed obvious difference though the closure did not change the sequence of the five pollutants' concentrations in the air at diverse sampling moments. The changing of the 24-h average concentrations of the five pollutants indicated the amount of pollutants in the air were greatly affected by human activities. The nitrogen dioxide, the sulfur dioxide and the particulate matters decreased obviously in the closure. The air in the metropolis and the south-east cities were relatively clean and the pollutants' concentrations decreased slightly during the closure period. The northern and the heavy industrial cities showed significant drop on air pollution indicators and the air quality of the two city groups could be greatly improved if some effective measures could be taken of environmental management and regional development.

Oriented-Structured CsCu2I3 Film by Close-Space Sublimation and Nanoscale Seed Screening for High-Resolution X-ray Imaging

An all-inorganic lead-free halides Cs-Cu-I system, represented by Cs₃Cu₂I₅ and CsCu₂I₃, has attracted attention for their good photophysical characteristics recently. Successive works had reported their application potential in light-emitting devices. However, there is no report for CsCu₂I₃ in X-ray scintillation detectors so far. We notice that CsCu₂I₃ may be advantageous in such an application due to the one-dimensional crystal structure, the congruent-melting feature, and the high spectral matching to some photosensors. In this work, we explore the scintillation properties and imaging application of CsCu₂I₃ in X-ray scintillator detector. The oriented structure is designed to enhance the imaging performance of a CsCu₂I₃ detector. Close-space sublimation process and nanoscale seed screening strategy are employed to realize this design by producing a large-area (25 cm²) CsCu₂I₃ thick film layer with the oriented nanorod structure. This CsCu₂I₃ detector eventually achieves a high spatial resolution of 7.5 lp mm^-1 in X-ray imaging.

Lead-Free Perovskite Variant Solid Solutions Cs2 Sn1- x Tex Cl6 : Bright Luminescence and High Anti-Water Stability

Underwater lighting is important for the exploration of the underwater world in different areas. It is of great significance for developing underwater emitters with high penetrability, high luminous efficiency, good anti-water stability, and environmental friendliness. Stable lead-free perovskite luminescent materials, represented by vacancy-ordered double perovskites, are worthy of research because they can almost meet the above requirements. Here, lead-free perovskite variant solid solutions with the formula of Cs₂ Sn_{1- x} Te_x Cl₆ are reported. Upon the exchange of Sn/Te ions, strong Jahn-Teller distortion of octahedra occurs in the lattice structure. The combination of Te luminescent center and Jahn-Teller-like self-trapped excitons gives this material yellow-green luminescence with a wavelength of 580 nm and a high photoluminescence quantum yield of 95.4%. Moreover, these solid solutions can withstand the extreme conditions of immersion in water probably due to the formation of amorphous alteration phase. Such good anti-water stability is also supported by the molecule dynamics simulation result that no reaction occurs on the water/Cs₂ SnCl₆ interface. The high luminous, suitable wavelength, and good anti-water stability enable the solid solutions suitable for the application for underwater lighting.

Efficient and Reabsorption-Free Radioluminescence in Cs3Cu2I5 Nanocrystals with Self-Trapped Excitons

Radioluminescent materials (scintillators) are widely applied in medical imaging, nondestructive testing, security inspection, nuclear and radiation industries, and scientific research. Recently, all-inorganic lead halide perovskite nanocrystal (NC) scintillators have attracted great attention due to their facile solution processability and ultrasensitive X-ray detection, which allows for large area and flexible X-ray imaging. However, the light yield of these perovskite NCs is relatively low because of the strong self-absorption that reduces the light out-coupling efficiency. Here, NCs with self-trapped excitons emission are demonstrated to be sensitive, reabsorption-free scintillators. Highly luminescent and stable Cs3Cu2I5 NCs with a photoluminescence quantum yields of 73.7%, which is a new record for blue emission lead-free perovskite or perovskite-like NCs, is produced with the assistance of InI3. The PL peak of the Cs3Cu2I5 NCs locates at 445 nm that matches with the response peak of a silicon photomultiplier. Thus, Cs3Cu2I5 NCs are demonstrated as efficient scintillators with zero self-absorption and extremely high light yield (≈79 279 photons per MeV). Both Cs3Cu2I5 NC colloidal solution and film exhibit strong radioluminescence under X-ray irradiation. The potential application of Cs3Cu2I5 NCs as reabsorption-free, low cost, large area, and flexible scintillators is demonstrated by a prototype X-ray imaging with a high spatial resolution.

High-Quality MAPbBr3 Cuboid Film with Promising Optoelectronic Properties Prepared by a Hot Methylamine Precursor Approach

Though CH₃NH₃PbBr₃ single crystals are frequently applied in various optoelectronic devices due to their favorable cuboid geometry, superior optoelectronic properties, and better stability than CH₃NH₃PbI₃, CH₃NH₃PbBr₃ polycrystalline films normally show poorer morphology with scattered crystals than their iodide counterparts, inherently due to their different crystallization habits. In this work, a facile process based on a hot methylamine-based precursor with high viscosity and concentration is demonstrated to counteract rapid ion diffusion. The precursor also has special features including a large colloidal size, a solid form at room temperature, and fast crystallization offered by the easy evacuation of methylamine. CH₃NH₃PbBr₃ films composed of tightly aligned CH₃NH₃PbBr₃ cuboids on micron scale are obtained. Wide channel (100 μm) photodetectors made from the CH₃NH₃PbBr₃ films show promising photoresponse and fast response speeds on par with those based on single crystals, suggesting high film quality and good optoelectronic connections between neighboring cuboids.

Reversible luminescent humidity chromism of organic-inorganic hybrid PEA2MnBr4 single crystals

Organic-inorganic hybrids have drawn great attention for gas sensors due to their high sensitivity, good selectivity and acceptable stability at room temperature. There are two main approaches by which organic-inorganic hybrids convert gas information to electric or optical signals (vapochromism). Here, we have reported a new organic-inorganic hybrid PEA₂MnBr₄ for humidity detection by luminescent visible chromism. PEA₂MnBr₄ single crystals were grown by the solution method and determined by single-crystal X-ray diffraction. Luminescent humidity chromism was found on PEA₂MnBr₄ from green emission at the water-desorption state to pink emission at the water-adsorption state within 18 s at a relative humidity of 38% RH. This obviously visible chromism was further used to check the water content in toluene with a low detection limit between 0.02 and 0.05 vol%.

All-Inorganic Copper Halide as a Stable and Self-Absorption-Free X-ray Scintillator

Lead halide perovskites have recently shown great potential as X-ray scintillators; however, the toxicity of the lead element seriously restricts their applications. Herein we report a new lead-free and self-absorption-free scintillator based on Rb₂CuCl₃ metal halide. The Rb₂CuCl₃ exhibits a near-unity photoluminescence quantum yield (99.4%) as well as a long photoluminescence lifetime (11.3 μs). Furthermore, Rb₂CuCl₃ demonstrates an appreciable light yield of 16 600 photons per megaelectronvolt and a large scintillation response with a linear range from 48.6 nGy_air s^-1 to 15.7 μGy_air s^-1. Notably, the detection limit is as low as 88.5 nGy_air s^-1, enabling a reduced radiation dose to the human body when a medical and security check is conducted. In addition, Rb₂CuCl₃ exhibits good stability against the atmosphere, continuous ultraviolet light, as well as X-ray irradiation. The combination of the decent scintillation performance, low toxicity and good stability suggests the Rb₂CuCl₃ could be a possible promising X-ray scintillator.

Circularly Polarized Luminescence from Chiral Tetranuclear Copper(I) Iodide Clusters

Circularly polarized luminescent (CPL) materials are promising in applications such as 3D displays and quantum communication. Hybrid organic-inorganic copper(I) iodides have been rapidly developed due to their intense photoluminescence and structural diversity; nevertheless, the reported Cu-I clusters rarely show CPL activities. In this study, we introduced chiral organic molecules R/S-methylbenzylammonium (R/S-MBA) into Cu-I inorganic skeletons to achieve chiral tetranuclear (R/S-MBA)₄Cu₄I₄ clusters with intense orange luminescence and CPL activity at room temperature. These enantiomeric (R/S-MBA)₄Cu₄I₄ clusters show oppositely signed circular dichroism (CD) signals, which agree well with their simulated electronic CD spectra. The crystallization-induced helical arrangement of (R/S-MBA)₄Cu₄I₄ clusters and their largely distorted polynuclear configuration demonstrate a new platform for the study of chiral-related properties.

Efficient PbSe Colloidal Quantum Dot Solar Cells Using SnO2 as a Buffer Layer

PbSe colloidal quantum dots (CQDs) are widely used in solar cells because of their tunable band gap, solution processability, and efficient multiple exciton generation effect. The most efficient PbSe CQD solar cells use high-temperature-processed ZnO as the electron transport layer (ETL), limiting their applications in flexible photovoltaics. Currently, low-temperature solution-processed SnO₂ has been demonstrated as an efficient ETL for high-efficient PbS CQD and perovskite solar cells because of less parasitic light absorption and higher electron mobility. Herein, we introduce low-temperature solution-processed SnO₂ as ETL for PbSe CQD solar cells, and fabricate the PbSe CQD absorber layer with a one-step spin-coating method. The champion device with the structure of FTO (SnO₂:F)/SnO₂/PbSe-PbI₂/PbS-EDT (1,2-ethanedithiol)/Au achieves a high open-circuit voltage of 577.1 mV, a short-circuit current density of 24.87 mA  cm^-2, a fill factor of 67%, and an impressive power conversion efficiency of 9.67%. Our results pave the way for the development of low-temperature flexible PbSe CQD solar cells.

Rubidium Doping to Enhance Carrier Transport in CsPbBr3 Single Crystals for High-Performance X-Ray Detection

The direct band gap CsPbBr₃ perovskite is regarded as a promising alternative for low-cost and high-performance X-ray radiation detectors. Despite the fact that CsPbBr₃ nanocrystals have been shown to be good scintillators in the indirect conversion mode, the direct X-ray conversion with CsPbBr₃ single crystals is expected to yield higher spatial resolution. Here, rubidium (Rb) doping is demonstrated to be an efficient approach to improve carrier transport and X-ray detection performance in the direct-conversion X-ray detectors based on Cs_(1-x)Rb_xPbBr₃ single crystals. Electrical properties' characterizations as combined with X-ray photoelectron spectroscopy (XPS) measurements have revealed that Rb doping in Cs_(1-x)Rb_xPbBr₃ single crystals can enhance the atomic interaction and orbital coupling between Pb and Br atoms, leading to an enhancement of carrier transport and X-ray detection performance. X-ray detectors based on a small amount (0.037%) of Rb-doped Cs_(1-x)Rb_xPbBr₃ single crystals exhibited a high X-ray sensitivity of 8097 μC Gy_air^-1 cm^-2. This work offers a feasible strategy to improve the X-ray detection performance by chemical doping in all-inorganic perovskite X-ray detectors.

Hot-Pressed CsPbBr3 Quasi-Monocrystalline Film for Sensitive Direct X-ray Detection

An X-ray detector with high sensitivity would be able to increase the generated signal and reduce the dose rate; thus, this type of detector is beneficial for applications such as medical imaging and product inspection. The inorganic lead halide perovskite CsPbBr₃ possesses relatively larger density and a higher atomic number in contrast to its hybrid counterpart. Therefore, it is expected to provide high detection sensitivity for X-rays; however, it has rarely been studied as a direct X-ray detector. Here, a hot-pressing method is employed to fabricate thick quasi-monocrystalline CsPbBr₃ films, and a record sensitivity of 55 684 µC Gy_air ^-1 cm^-2 is achieved, surpassing all other X-ray detectors (direct and indirect). The hot-pressing method is simple and produces thick quasi-monocrystalline CsPbBr₃ films with uniform orientations. The high crystalline quality of the CsPbBr₃ films and the formation of self-formed shallow bromide vacancy defects during the high-temperature process result in a large µτ product and, therefore, a high photoconductivity gain factor and high detection sensitivity. The detectors also exhibit relatively fast response speed, negligible baseline drift, and good stability, making a CsPbBr₃ X-ray detector extremely competitive for high-contrast X-ray detections.

Lead-Free Halide Rb2 CuBr3 as Sensitive X-Ray Scintillator

Scintillators are widely utilized for radiation detections in many fields, such as nondestructive inspection, medical imaging, and space exploration. Lead halide perovskite scintillators have recently received extensive research attention owing to their tunable emission wavelength, low detection limit, and ease of fabrication. However, the low light yields toward X-ray irradiation and the lead toxicity of these perovskites severely restricts their practical application. A novel lead-free halide is presented, namely Rb₂ CuBr₃ , as a scintillator with exceptionally high light yield. Rb₂ CuBr₃ exhibits a 1D crystal structure and enjoys strong carrier confinement and near-unity photoluminescence quantum yield (98.6%) in violet emission. The high photoluminescence quantum yield combined with negligible self-absorption from self-trapped exciton emission and strong X-ray absorption capability enables a record high light yield of ≈91056 photons per MeV among perovskite and relative scintillators. Overall, Rb₂ CuBr₃ provides nontoxicity, high radioluminescence intensity, and good stability, thus laying good foundations for potential application in low-dose radiography.

Broadband emission of double perovskite Cs2Na0.4Ag0.6In0.995Bi0.005Cl6:Mn2+ for single-phosphor white-light-emitting diodes

In this Letter, we report the broadband photoluminescence of lead-free double perovskite Cs₂Na_0.4Ag_0.6In_0.95Bi_0.05Cl₆:Mn²⁺. Under ultraviolet excitation, the white phosphor shows two emission peaks at 550 nm and 610 nm from self-trapped exciton and doped Mn²⁺ ions, respectively, leading to a broad emission spectrum over the whole visible spectrum suitable for lighting application. The white-light-emitting diodes exhibit high light quality with CIE coordinates (0.38, 0.42) and color rendering index of 82.6. The mechanism of luminescence of this double perovskite is also discussed in this Letter.

Tunable Color Temperatures and Efficient White Emission from Cs2 Ag1- x Nax In1- y Biy Cl6 Double Perovskite Nanocrystals

Recently, Bi-doped Cs₂ Ag_0.6 Na_0.4 InCl₆ lead-free double perovskites demonstrating efficient warm-white emission have been reported. To enable the solution processing and enrich the application fields of this promising material, here a colloidal synthesis of Cs₂ Ag_{1- x} Na_x In_{1- y} Bi_y Cl₆ nanocrystals is further developed. Different from its bulk states, the emission color temperatures of the nanocrystal can be tuned from 9759.7 to 4429.2 K by Na⁺ and Bi³⁺ incorporation. Furthermore, the newly developed nanocrystals can break the wavefunction symmetry of the self-trapped excitons by partial replacement of Ag⁺ ions with Na⁺ ions and consequently allow radiative recombination. Assisted with Bi³⁺ ions doping and ligand passivation, the photoluminescence quantum yield of the Cs₂ Ag_0.17 Na_0.83 In_0.88 Bi_0.12 Cl₆ nanocrystals is further promoted to 64%, which is the highest value for lead-free perovskite nanocrystals at present. The new colloidal nanocrystals with tunable color temperature and efficient photoluminescence are expected to greatly advance the research progress of lead-free perovskites in single-emitter-based white emitting materials and devices.

Lead-Free Halide Perovskites and Perovskite Variants as Phosphors toward Light-Emitting Applications

Lead halide perovskites have attracted tremendous research interests in the light-emitting field because of their high defect tolerance, solution processability, tunable spectrum, and efficient emission. In terms of luminescence types, both the narrowband emission derived from free-exciton (FE) and broadband white light emission from self-trapped exciton (STE) show great advantages in light-emitting applications. Despite the fascinating characteristics, their commercialization still suffers from the presence of toxic lead (Pb) and unsatisfactory stability. In this spotlight, we mainly focus on the lead-free candidates as phosphors for possible light-emitting applications. Thanks to the chemical diversity of metal halide perovskites and perovskite variants, many excellent lead-free light-emitting materials have recently been synthesized and characterized. We first classify these materials into three types according to material structures, including (1) double perovskites A₂B(I)B(III)X₆, (2) vacancy ordered perovskites A₂B(IV)X₆, (3) miscellaneous perovskite variants or halide semiconductors, which refer to halides without clear relation to the perovskite structure. We then highlight the importance of electronic dimensionality, defect passivation, and impurity doping in developing highly efficient perovskite-based emitters. We also discuss their applications in white light-emitting diodes (W-LED). Further challenges toward practical applications and potential applications are also included in a section on outlook and future challenges.

Inorganic antimony halide hybrids with broad yellow emissions

Lead halide perovskites exhibit unexceptionable photoelectric properties. However, these materials are unsatisfactory in terms of stability and toxicity. Herein, we report Rb₇Sb₃Cl₁₆ as a new kind of lead free perovskite variants. This material can be easily obtained through hydrothermal reactions. The composition is determined through structure refinement, elemental analysis and X-ray photoelectron spectra. Rb₇Sb₃Cl₁₆ exhibits a broad yellow emission at 560 nm, with a Stokes shift of 175 nm and a photoluminescence quantum yield (PLQY) around 26%. Rb₇Sb₃Cl₁₆ also shows good thermal and water stability due to its inorganic composition. White light-emitting diodes (LEDs) are constructed by combining Rb₇Sb₃Cl₁₆ as yellow phosphors, our previously reported Cs₂SnCl₆:2.75%Bi as blue phosphors, and commercial UV LED chips as the excitation source, producing a white light with the Commission Internationale de'Eclairage (CIE) color coordinates at (0.39, 0.38).

Heteroepitaxial passivation of Cs2AgBiBr6 wafers with suppressed ionic migration for X-ray imaging

X-ray detectors are broadly utilized in medical imaging and product inspection. Halide perovskites recently demonstrate excellent performance for direct X-ray detection. However, ionic migration causes large noise and baseline drift, limiting the detection and imaging performance. Here we largely eliminate the ionic migration in cesium silver bismuth bromide (Cs2AgBiBr6) polycrystalline wafers by introducing bismuth oxybromide (BiOBr) as heteroepitaxial passivation layers. Good lattice match between BiOBr and Cs2AgBiBr6 enables complete defect passivation and suppressed ionic migration. The detector hence achieves outstanding balanced performance with a signal drifting one order of magnitude lower than all previous studies, low noise (1/f noise free), a high sensitivity of 250 µC Gy air-1 cm-2, and a spatial resolution of 4.9 lp mm-1. The wafer area could be easily scaled up by the isostatic-pressing method, together with the heteroepitaxial passivation, strengthens the competitiveness of Cs2AgBiBr6-based X-ray detectors as next-generation X-ray imaging flat panels.