Dion-Jacobson Type Lead-Free Double Perovskite with Ultra-Narrow Aromatic Interlayer Spacing for Highly Sensitive and Stable X-ray Detection

The low-toxic and environmentally friendly 2D lead-free perovskite has made significant progress in the exploration of "green" X-ray detectors. However, the gap in detection performance between them and their lead-based analogues remains a matter of concern that cannot be ignored. To reduce this gap, shortening the interlayer spacing to accelerate the migration and collection of X-ray carriers is a promising strategy. Herein, a Dion-Jacobson (DJ) lead-free double perovskite (4-AP)2 AgBiBr8 (1, 4-AP = 4-amidinopyridine) with an ultra-narrow interlayer spacing of 3.0 Å, is constructed by utilizing π-conjugated aromatic spacers. Strikingly, the subsequent enhanced carrier transport and increased crystal density lead to X-ray detectors based on bulk single crystals of 1 with a high sensitivity of 1117.3 µC Gy-1  cm-2 , superior to the vast majority of similar double perovskites. In particular, the tight connection of the inorganic layers by the divalent cations enhances structural rigidity and stability, further endowing 1 detector with ultralow dark current drift (3.06 × 10-8  nA cm-1  s-1  V-1 , 80 V), excellent multiple cycles switching X-ray irradiation stability, as well as long-term environmental stability (maintains over 94% photoresponse after 90 days). This work brings lead-free double perovskites one step closer to realizing efficient practical green applications.

Micro/Nano Perovskite Materials for Advanced X-ray Detection and Imaging

Halide perovskites have emerged as highly promising materials for ionizing radiation detection due to their exceptional characteristics, including a large mobility-lifetime product, strong stopping power, tunable band gap, and cost-effective crystal growth via solution processes. Semiconductor-type X-ray detectors employing various micro/nano perovskite materials have shown impressive progress in achieving heightened sensitivity and lower detection limits. Here, we present a comprehensive review of the applications of micro/nano perovskite materials for direct type X-ray detection, with a focus on the requirements for micro/nano crystal assembly and device properties in advanced X-ray detectors. We explore diverse processing techniques and optoelectronic considerations applied to perovskite X-ray detectors. Additionally, this review highlights the challenges and promising opportunities for perovskite X-ray detector arrays in real-world applications, potentially necessitating further research efforts.

Molecular Design of Layered Hybrid Silver Bismuth Bromine Single Crystal for Ultra-Stable X-Ray Detection With Record Sensitivity

Nowadays, weak interlayer coupling and unclear mechanism in layered hybrid silver bismuth bromine (LH-AgBiBr) are the main reasons for limiting its further enhanced X-ray detection sensitivity and stability. Herein, the design rules for LH-AgBiBr and its influence on X-ray detection performance are reported for the first time. Although shortening amine size can enhance interlayer coupling, its detection performance is severely hampered by its easier defect formation caused by enlarged micro strain. In contrast, an appropriate divalent amine design endows the material with improved interlayer coupling and released micro strain, which benefits crystal stability and mechanical hardness. Another contribution is to increase material density and dielectric constant; thus, enhancing X-ray absorption and carrier transport. Consequently, the optimized parallel device based on BDA2 AgBiBr8 achieves a record sensitivity of 2638 µC Gyair -1 cm-2 and an ultra-low detection limit of 7.4 nGyair s-1 , outperforming other reported LH-AgBiBr X-ray detectors. Moreover, the unencapsulated device displays remarkable anti-moisture, anti-thermal (>150 °C), and anti-radiation (>1000 Gyair ) endurance. Eventually, high-resolution hard X-ray imaging is demonstrated by linear detector arrays under a benign dose rate (1.63 µGyair s-1 ) and low external bias (5 V). Hence, these findings provide guidelines for future materials design and device optimization.

Heterointerface Design of Perovskite Single Crystals for High-Performance X-Ray Imaging

Metal halide perovskite single crystals (MHP-SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility-lifetime products and strong X-ray absorption, they are considered promising materials for efficient X-ray detection. However, they suffer from large dark currents and severe ion migration, which limit their sensitivity and stability in critical X-ray detection applications. Herein, a heterointerface design is proposed to reduce both the dark current and ion migration by forming a heterojunction. In addition, the carrier transport performance is significantly improved using heterointerface engineering by designing a gradient band structure in the SCs. The SC heterojunction detectors exhibit a high sensitivity of 3.98 × 105 µC Gyair -1 cm-2 with a low detection limit of 12.2 nGyair s-1 and a high spatial resolution of 10.2 lp mm-1 during imaging. These values are among the highest reported for state-of-the-art MHP X-ray detectors. Moreover, the detectors show excellent stability under continuous X-ray irradiation and maintainclear X-ray imaging after 240 d. This study provides novel insights into the design and fabrication of X-ray detectors with high detection efficiency and stability, which are beneficial for developing inexpensive, high-resolution X-ray imaging equipment.

A New Metal-Free Molecular Perovskite-Related Single Crystal with Quantum Wire Structure for High-Performance X-Ray Detection

The family of metal-free molecular perovskites, an emerging novel class of eco-friendly semiconductor, welcomes a new member with a unique 1D hexagonal perovskite structure. Lowering dimensionality at molecular level is a facile strategy for crystal structure conversion, optoelectronic property regulation, and device performance optimization. Herein, the study reports the design, synthesis, packing structure, and photophysical properties of the 1D metal-free molecular perovskite-related single crystal, rac-3APD-NH4 I3 (rac-3APD= racemic-3-Aminopiperidinium), that features a quantum wire structure formed by infinite chains of face-sharing NH4 I6 octahedra, enabling strong quantum confinement with strongly self-trapped excited (STE) states to give efficient warm orange emission with a photoluminescence quantum yield (PLQY) as high as ≈41.6%. The study accordingly unveils its photoexcited carrier dynamics: rac-3APD-NH4 I3 relaxes to STE state with a short lifetime of 10 ps but decays to ground state by emitting photons with a relatively longer lifetime of 560 ps. Additionally, strong quantum confinement effect is conducive to charge transport along the octahedral channels that enables the co-planar single-crystal X-ray detectors to achieve a sensitivity as high as 1556 µC Gyair -1 cm-2 . This work demonstrates the first case of photoluminescence mechanism and photophysical dynamics of 1D metal-free perovskite-related semiconductor, as well as the promise for high-performance X-ray detector.

Metal-Free Hydrazinium Halide Perovskitoid Single Crystals for X-ray Detection

Metal-free perovskitoids (MFPs) with N2H5+ as B-site component possess higher crystal density and hydrogen bonding networks and have been recently expanded into X-ray detection. However, research on this material is in its infancy and lacks an understanding of the function of halide components on physical properties and device performance. Here, N2H5-based MFP single crystals (SCs) with different halides are fabricated, and the influence of halides on the crystal structure, band nature, charge transport characteristics, and final device performance is actively explored. Based on theory and experiments, the tolerance factor and octahedral factor jointly determine the octahedral composition. Further, halides with different electronegativities and ionic radii also affect octahedral distortion and energy band bending, further influencing carrier transport and device performance. Finally, a sensitivity of 1284 μC Gyair-1 cm-2 and low detection limits (LoD) of 5.62 μGyair s-1 were obtained by the Br-based device due to its superior physical properties.

Optimized Design of a Hexagonal Equal Gap Silicon Drift Detector with Arbitrary Surface Electric Field Spiral

In our previous studies, the silicon drift detector (SDD) structure with a constant spiral ring cathode gap (g) and a given surface electric field has been partially investigated based on the physical model that gives an analytical solution to the integrals in the calculations. Those results show that the detector has excellent electrical characteristics with a very homogeneous carrier drift electric field. In order to cope with the implementation of the theoretical approach with a complete set of technical parameters, this paper performs different theoretical algorithms for the technical implementation of the detector performance using the Taylor expansion method to construct a model for cases where the parameter "j" is a non-integer, approximating the solution with finite terms. To verify the accuracy of this situation, we performed a simulation of the relevant electrical properties using the Sentaurus TCAD tool 2018. The electrical properties of the single and double-sided detectors are first compared, and then the effects of different equal gaps g (g = 10 μm, 20 μm, and 25 μm, respectively) on the electrical properties of the double-sided detectors are analyzed and demonstrated. By analyzing and comparing the electrical characteristics data from the simulation results, we can show that the double-sided structure has a larger transverse drift electric field, which improves the spatial position resolution as well as the response speed. The effect of the gap size on the electrical characteristics of the detector is also analyzed by analyzing three different gap bifacial detectors, and the results show that a 10 μm equal gap is the optimal design. Such results can be used in applications requiring large-area SDD, such as the pulsar X-ray autonomous navigation. in the future to provide navigation and positioning space services for spacecraft deep-space exploration.

High-Efficiency Narrow-Band Green-Emitting Manganese(II) Halide for Multifunctional Applications

Zero-dimensional (0D) Mn2+-based metal halides used as luminescent materials and scintillators have become a research hotspot in the field of photoelectric materials and devices due to their unique composition, structure, and fluorescence properties. It is of great value to explore new Mn2+-based metal halides to achieve multifunctional applications. Herein, the novel 0D Mn2+-based metal halide single crystal (BPTP)2MnBr4 is synthesized by a simple solvent-antisolvent recrystallization method. Under excitation at 468 nm, the (BPTP)2MnBr4 single crystal shows a pronounced narrow-band green luminescence centered at 515 nm derived from the d-d transition of the Mn2+ ion. This emission has a relatively narrow full width at half maximum of 43 nm and a high photoluminescence quantum yield (PLQY) of 82%. In addition, (BPTP)2MnBr4 exhibits good thermal stability at 393 K with a retention of 79% of the initial photoluminescence intensity at 298 K. Benefiting from its strong blue light excitation, high PLQY, and good thermal stability, we manufacture an ideal white light-emitting diode (LED) device using a 460 nm blue LED chip, green-emitting (BPTP)2MnBr4, and commercial K2SiF6:Mn4+ red phosphor. Under 20 mA drive current, the LED shows a high luminous efficiency of 112 lm/W and a wide color gamut of 110.8%, according to the National Television System Committee standard. In addition, (BPTP)2MnBr4 crystals show a strong X-ray absorption. Based on the commercial Lu3Al5O12:Ce3+ scintillator, the calculated light yield of (BPTP)2MnBr4 reaches up to about 136,000 photons/MeV and the detection limit reaches 0.282 μGyair s-1. Additionally, a melt quenching approach is used to construct a (BPTP)2MnBr4 clear glass scintillation screen, realizing a spatial resolution of 10.1 lp/mm. The proper performances of (BPTP)2MnBr4 as phosphor-converted LED materials and the X-ray scintillator with the addition of eco-friendly, low-cost solution processability make 0D Mn2+-based metal halides potential luminescent materials for multifunctional applications.

Metal-Free Perovskites for X-Ray Detection

Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials' stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.

Highly Sensitive Direct X-Ray Detector Based on Copper(II) Coordination Polymer Single Crystal with Anisotropic Charge Transport

Anisotropic charge transport plays a pivotal role in clarifying the conductivity mechanism in direct X-ray detection to improve the detection sensitivity. However, the anisotropic photoelectric effect of semiconductive single crystal responsive to X-ray is still lacking of theoretical and experimental proof. The semiconductive coordination polymers (CPs) with designable structures, adjustable functions, and high crystallinity provide a suitable platform for exploring the anisotropic conductive mechanism. Here,the study first reveals a 1D conductive transmission path for direct X-ray detection from the perspective of structural chemistry. The semiconductive copper(II)-based CP 1 single crystal detector exhibits unique anisotropic X-ray detection performance. Along the 1D π-π stacking direction, the single crystal device (1-SC-a) shows a superior sensitivity of 2697.15 µCGyair -1  cm-2 and a low detection limit of 1.02 µGyair  s-1 among CPs-based X-ray detectors. This study provides beneficial guidance and deep insight for designing high-performance CP-based X-ray detectors.

X-Site Substituted 2D Cs2 Pb(SCN)2 Br2 Perovskites for X-Ray Detection

2D Ruddlesden-Popper (RP) perovskites have been intensively investigated due to their superior stability and outstanding optoelectrical properties. However, investigations on 2D RP perovskites are mainly focused on A-site substituted perovskites and few reports are on X-site substituted perovskites especially in X-ray detection field. Here, X-site substituted 2D RP perovskite Cs2 Pb(SCN)2 Br2 polycrystalline wafers are prepared and systematically studied for X-ray detection. The obtained wafers show a large resistivity of 2.0 × 1010 Ω cm, a high ion activation energy of 0.75 eV, a small current drift of 2.39 × 10-6 nA cm-1 s-1 V-1 , and charge carrier mobility-lifetime product under X-ray as high as 1.29 × 10-4 cm2 V-1 . These merits enable Cs2 Pb(SCN)2 Br2 wafer detectors with a sensitivity of 216.3 µC Gyair -1 cm-2 , a limit of detection of 42.4 nGyair s-1 , and good imaging ability with high spatial resolution of 1.08 lp mm-1 . In addition, Cs2 Pb(SCN)2 Br2 wafer detectors demonstrate excellent operational stability under high working field up to 2100 V cm-1 after continuous X-ray irradiation with a total dose of 45.2 Gyair . The promising features such as short octahedral spacing and weak ion migration will open up a new perspective and opportunity for SCN-based 2D perovskites in X-ray detection.

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

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

Weak X-Ray to Visible Lights Detection Enabled by a 2D Multilayered Lead Iodide Perovskite with Iodine-Substituted Spacer

Broadband photodetectors (PDs) with low detection limits hold significant importance to next-generation optoelectronic devices. However, simultaneously detecting broadband (i.e., X-ray to visible regimes) and weak lights in a single semiconducting material remains highly challenging. Here, by alloying iodine-substituted short-chain cations into the 3D FAPbI₃ (FA = formamidine), a new 2D bilayered lead iodide hybrid perovskite, (2IPA)₂ FAPb₂ I₇ (1, 2IPA = 2-iodopropylammonium), that enables addressing this challenge is reported. Such a 2D multilayered structure and lead iodide composition jointly endow 1 with a minimized dark current (6.04 pA), excellent electrical property, and narrow bandgap (2.03 eV), which further gives it great potential for detecting broadband weak lights. Consequently, its high-quality single crystal PDs exhibit remarkable photoresponses to weak ultraviolet-visible lights (377-637 nm) at several tens of nW cm^-2 with high responsivities (>10²  mA W^-1 ) and significant detectivities (>10¹² Jones). Moreover, 1 has an excellent X-ray detection performance with a high sensitivity of 438 µC Gy^-1 cm^-2 and an ultralow detection limit of 20 nGy s^-1 . These exceptional attributes make 1 a promising material for broadband weak lights detection, which also sheds light on future explorations of high-performance PDs based on 2D hybrid perovskites.

Wide-Bandgap Rare-Earth Iodate Single Crystals for Superior X-Ray Detection and Imaging

Semiconductor-based X-ray detectors with low detectable thresholds become critical in medical radiography applications. However, their performance is generally limited by intrinsic defects or unresolved issues of materials, and developing a novel scintillation semiconductor for low-dose X-ray detection is a highly urgent objective. Herein, a high-quality rare-earth iodate Tm(IO₃ )₃ single crystal grown through low-cost solution processing is reported with a wide bandgap of 4.1 eV and a large atomic number of 53.2. The roles of IO and TmO groups for charge transport in the Tm(IO₃ )₃ are revealed with the structural difference between the [101] and [ 1 ¯ 01 ] $[{\bar{1}}01]$ crystal orientations. Based on anisotropic responses of material properties and detection performances, it is found that the [ 1 ¯ 01 ${\bar{1}}01$ ] orientation, the path with fewer IO groups, achieves a high resistivity of 1.02 × 10¹¹ Ω cm. Consequently, a single-crystal detector exhibits a low dark current and small baseline drifting due to the wide bandgap, high resistivity and less ion migration of Tm(IO₃ )₃ , resulting in a low detection limit of 85.2 nGy_air s^-1 . An excellent X-ray imaging performance with a high sensitivity of 4406.6 µC Gy_air ^-1 cm^-2 is also shown in the Tm(IO₃ )₃ device. These findings provide a new material design perspective for high-performance X-ray imaging applications.

Photodarkening, Photobrightening, and the Role of Color Centers in Emerging Applications of Lanthanide-Based Upconverting Nanomaterials

Upconverting nanoparticles (UCNPs) compose a class of luminescent materials that utilize the unique wavelength-converting properties of lanthanide (Ln) ions for light-harvesting applications, photonics technologies, and biological imaging and sensing experiments. Recent advances in UCNP design have shed light on the properties of local color centers, both intrinsic and controllably induced, within these materials and their potential influence on UCNP photophysics. In this review, we describe fundamental studies of color centers in Ln-based materials, including research into their origins and their roles in observed photodarkening and photobrightening mechanisms. We place particular focus on the new functionalities that are enabled by harnessing the properties of color centers within Ln-doped nanocrystals, illustrated through applications in afterglow-based bioimaging, X-ray detection, all-inorganic nanocrystal photoswitching, and fully rewritable optical patterning and memory.

Phenyl-Terminated Coupling Interface Enabled Highly Efficient and Stable Multiwavelength Perovskite Single Crystal/Silicon Integrated Photodetector

The use of amino-terminated siloxanes as coupling interface for perovskite single crystals (PSCs)/silicon integrated devices has been demonstrated to be an effective method toward CMOS compatible optoelectronics; however, it suffers from the coupling stability against the hydrophilicity of the exposed terminal amino groups. In this work, a phenyl-terminated interfacial molecule, anilino-methyl-triethoxysilane (AMTES), is proposed to achieve the effectively galvanic coupling between PSCs and silicon, which can not only improve the device environmental reliability but also lower the surface energy of the silicon substrate so as to facilitate the epitaxial growth of PSCs. Benefiting from the interfacial coupling of AMTES, the obtained MAPbI₃ SC/silicon integrated device possesses highly efficient multiwavelength photodetection properties across the X-ray and NIR range, which exhibits a specific detectivity D* of 3.84 × 10¹³ cm Hz^1/2 W^-1 in the visible-NIR region and an X-ray sensitivity of 1.18 × 10⁴ μC Gy_air^-1 cm^-2 with the lowest detection limit of 49.6 nGy_air s^-1. The ultra wide -3 dB bandwidth of 67,300 Hz and the linear dynamic range (LDR) of 112 dB also prove its impressive dynamic response capabilities. Moreover, the AMTES modified integrated device almost maintains 96% of the initial photodetection performance even after keeping in the atmosphere environment for 28 days. This work opens a new avenue for interfacial engineering toward the development of on-chip PSC integrated silicon optoelectronic devices.

Improving the Performance and High-Field Stability of FAPbBr3 Single Crystals in X-Ray Detection with Chenodeoxycholic Acid Additive

Organometal halide perovskite single crystals are one of the most promising radiation detection materials due to their unique advantages of high absorption coefficient, long carrier diffusion length, and low defect density. However, the severe ion migration in perovskites deteriorates the X-ray detection performance under longtime and high-field operating conditions. This work reports an effective additive of chenodeoxycholic acid (CDCA), which can suppress the ion migration and improve the performance and the operational stability of FAPbBr₃ single crystals (SCs) in X-ray detection significantl. The CDCA molecules in precursors effectively suppress the decomposition of FA ions, resulting in a better crystal orientation and stoichiometry. The trace amounts of CDCA residues in FAPbBr₃ SCs improve the thermal stability and effectively suppress the ion migration. The resulting detector shows an impressive X-ray sensitivity up to 21 386.88 µC Gy_air ^-1 cm^-2 under -500 V and a detection limit of 15.23 nGy_air s^-1 . The response current of the detector at 225 V cm^-1 field is barely changed under the 7200 s irradiation with a dose rate of 1.949 mGy_air s^-1 . This work provides insights for the additive selection and improving the operational stability of perovskite single crystals for commercial applications.

Electron-Phonon Coupling Suppression by Enhanced Lattice Rigidity in 2D Perovskite Single Crystals for High-Performance X-Ray Detection

2D Dion-Jacobson (DJ) perovskite single crystals (PSCs) usually demonstrate better X-ray detection performance than Ruddlesden-Popper (RP) PSCs. However, the mechanism of the improved performance is still elusive. Here, by the aid of strong interactions between dimethylbiguanide (DGA) and PbI₂ , a novel DJ-perovskitoid (DGA)PbI₄ is designed. From the comparison of (DGA)PbI₄ to other 2D PSCs, it is discovered that the tiniest lattice distortion and increased hydrogen bonds in the atom-scaled analysis strengthen lattice rigidity and weaken electron-phonon coupling to suppress disordered scattering of carriers, resulting in significantly improved carrier transport and stability. Therefore, high carrier mobility (78.1 cm² V^-1 s^-1 ) and a pronounced sensitivity of 4869.0 µC Gy_air ^-1 cm^-2 are achieved using (DGA)PbI₄ , which are the best in 2D Pb-based PSC devices to date. Finally, the (DGA)PbI₄ devices exhibit good spatial resolution in X-ray imaging and excellent long-term stability to work as a promising candidate for medical diagnostics and nondestructive determination.

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.

Oriented preparation of Large-Area uniform Cs2TeI6 perovskite film for high performance X-ray detector

Large-area flexible perovskite films are attracting widespread research interest for applications in wearable solar cells, portable photodetectors, bendable X-ray imaging detectors and other implantable optoelectronic devices. In this work, a facile mobile platform assisted electrospray method is developed to prepare large-area (100 cm²) lead-free Cs₂TeI₆ film on flexible polyimide substrate. The spraying parameters are coupled with the growth temperature to achieve a dynamic balance. The as-prepared film by optimized process shows high uniformity in grain size, thickness and X-ray response without pinholes and cracks. Moreover, oriented nucleation is more likely to occur on the flexible organic substrates for less growth stress and mismatch stress, leading to preferred (222) plane orientation. X-ray detectors prepared with the films exhibit a resistivity of 1.9 × 10¹¹ Ω·cm, an X-ray sensitivity of 226.8 μC⋅Gy_air^-1⋅cm^-2 and a transient response rise time as fast as 42 ms under 50 kV X-ray at an electrical field of 6.67 × 10³ V·mm^-1. The modified electrospray method shows great potential applications for large-area devices of radiography, solar cell and other optoelectronic devices.

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.

Flexible Scintillation Silica Fiber with Engineered Nanocrystals for Remote Real-Time X-ray Detection

Scintillation fibers based on rare-earth ion-doped crystal materials have attracted significant attention for applications in a wide range of areas from security to healthcare. However, the scintillation performance of crystal fibers is severely limited owing to the complex preparation process. Here, we report a modified preparation process of the transparent Ce/Tb co-doped yttrium pyrosilicate (YPS) nanocrystal silica fiber for the first time, which was fabricated by the CO₂ laser-heated method assisted with optimal thermal annealing. An YPS nanocrystal phase with an average size of approximately 38 nm is obtained by controlling the diffusion concentration of SiO₂ in the fiber core region. Both Ce³⁺ and Tb³⁺ ions were successfully embedded into YPS nanocrystals, which enhanced the energy transfer with an efficiency of 59.87% between the dopants as well as brighter green light emission. Furthermore, the X-ray-excited remote radioluminescence response of the obtained YPS nanocrystal fiber with a length of 20 m was approximately 1 order of magnitude larger than that of the precursor fiber, while the dose rate response exhibited excellent linearity. It is believed that the novel transparent YPS nanocrystal-doped silica optical fibers, combined with their excellent fluorescent properties, could be promising candidates for scintillators, fiber lasers, and phosphors.

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.

Simulating 50 keV X-ray Photon Detection in Silicon with a Down-Conversion Layer

Simulation results are presented that explore an innovative, new design for X-ray detection in the 20-50 keV range that is an alternative to traditional direct and indirect detection methods. Typical indirect detection using a scintillator must trade-off between absorption efficiency and spatial resolution. With a high-Z layer that down-converts incident photons on top of a silicon detector, this design has increased absorption efficiency without sacrificing spatial resolution. Simulation results elucidate the relationship between the thickness of each layer and the number of photoelectrons generated. Further, the physics behind the production of electron-hole pairs in the silicon layer is studied via a second model to shed more light on the detector's functionality. Together, the two models provide a greater understanding of this detector and reveal the potential of this novel form of X-ray detection.

Antisolvent-assisted Crystallization of Centimeter-sized Lead-free Bismuth Bromide Hybrid Perovskite Single Crystals with X-ray Sensitive Merits

Hybrid bismuth halides perovskites have emerged as promising candidates for X-ray detection, due to the strong absorptivity of high-energy X-ray photons, high resistivity, large carrier diffusion length and low toxicity. However, the mostly investigated hybrid bismuth iodides single crystals are usually opaque and require a harsh synthesis process. Herein, novel one-dimensional (1D) pentamethylenediamine bismuth bromide (PDA)BiBr₅ single crystals were synthesized via an antisolvent-assisted crystallization method at room temperature. Bulk (PDA)BiBr₅ single crystals have sizes of 10×1.3×1.5 mm³ and high transparency. They are shown to have low density of defects of 2.0×10¹⁰  cm^-3 and obvious photoconductivity. Moreover, they exhibit large bulk resistivity of 2.13×10¹¹  Ω cm and good X-ray attenuation coefficient. Consequently, the vertical structured (PDA)BiBr₅ single crystal X-ray photoconductor produces a sensitivity of 3.8 μC Gy_air ^-1  cm^-2 . This study provides a facile strategy for synthesizing bulk hybrid bismuth bromides single crystals with potential X-ray detection application.

Highly Luminescent Metal-Free Perovskite Single Crystal for Biocompatible X-Ray Detector to Attain Highest Sensitivity

Solution-processed metal-based halide perovskites have taken a dominant position for perovskite optoelectronics including light emission and X-ray detection; however, the toxicity of the included heavy metals severely restricts their applications for wearable, lightweight, and transient optoelectronic devices. Here, the authors describe investigations of large (4 × 6 × 2 mm³ ) 3D metal-free perovskite MDABCO-NH₄ I₃ (MDBACO = methyl-N'-diazabicyclo[2.2.2]octonium) single crystal and its charge recombination and extraction behavior for light emission and X-ray detection. Unlike conventional 3D metal-based perovskites, this lightweight and biocompatible perovskite large crystal is processed from aqueous solution at room temperature, and can achieve both an extremely long carrier lifetime up to ≈1.03 µs and the formation of self-trapped excited states for luminescence. These features contribute to a photoluminescence quantum yield (PLQY) as high as ≈53% at room temperature and an X-ray sensitivity up to 1997 ± 80 μC Gy cm^-2 at 50 V bias (highest among all metal-free detectors). The ability to tune the perovskite band gap by modulating the structure under high pressure is also demonstrated, which opens up applications for the crystal as colored emitters. These attributes make it a molecular alternative to metal-based perovskites for biocompatible and transient optoelectronics.

Mobile Ion-Driven Modulation of Electronic Conductivity Explains Long-Timescale Electrical Response in Lead Iodide Perovskite Thick Pellets

The favorable optoelectronic properties of metal halide perovskites have been used for X- and γ-ray detection, solar energy, and optoelectronics. Large electronic mobility, reduced recombination losses of the electron-hole pairs, and high sensitivity upon ionizing irradiation have fostered great attention on technological realizations. Nevertheless, the recognized mixed ionic-electronic transport properties of hybrid perovskites possess severe limitations as far as long-timescale instabilities and degradation issues are faced. Several effects are attributed to the presence of mobile ions such as shielding of the internal electrical field upon biasing and chemical interaction between intrinsic moving defects and electrode materials. Ion-originated modulations of electronic properties constitute an essential peace of knowledge to further progress into the halide perovskite device physics and operating modes. Here, ionic current and electronic impedance of lead methylammonium iodide perovskite thick pellets are independently monitored, showing self-consistent patterns. Our findings point to a coupling of ionic and electronic properties as a dynamic doping effect caused by moving ions that act as mobile dopants. The electronic doping profile changes within the bulk as a function of the actual ion inner distribution, then producing a specific time dependence in the electronic conductivity that reproduces time patterns of the type ∝t, a clear fingerprint of diffusive transport. Values for the iodine-related defect diffusivity in the range of D_ion ∼ 10^-8 cm² s^-1, which corresponds to ionic mobilities of about μ_ion ∼ 10^-6 cm² V^-1 s^-1, are encountered. Technological realizations based on thick perovskite layers would benefit from this fundamental information, as far as long-timescale current stabilization is concerned.

Dosimetry and Calorimetry Performance of a Scientific CMOS Camera for Environmental Monitoring

This paper explores the prospect of CMOS devices to assay lead in drinking water, using calorimetry. Lead occurs together with traces of radioisotopes, e.g., 210Pb, producing g-emissions with energies ranging from 10 keV to several 100 keV when they decay; this range is detectable in silicon sensors. In this paper we test a CMOS camera (OXFORD INSTRUMENTS Neo 5.5) for its general performance as a detector of X-rays and low energy g-rays and assess its sensitivity relative to the World Health Organization upper limit on lead in drinking water. Energies from 6 keV to 60 keV are examined. The CMOS camera has a linear energy response over this range and its energy resolution is for the most part slightly better than 2%. The Neo sCMOS is not sensitive to X-rays with energies below ~10 keV. The smallest detectable rate is 40 ± 3 mHz, corresponding to an incident activity on the chip of 7 ± 4 Bq. The estimation of the incident activity sensitivity from the detected activity relies on geometric acceptance and the measured efficiency vs. energy. We report the efficiency measurement, which is 0.08(2)% (0.0011(2)%) at 26.3 keV (59.5 keV). Taking calorimetric information into account we measure a minimal detectable rate of 4 ± 1 mHz (1.5 ± 0.1 mHz) for 26.3 keV (59.5 keV) g-rays, which corresponds to an incident activity of 1.0 ± 0.6 Bq (57 ± 33 Bq). Toy Monte Carlo and Geant4 simulations agree with these results. These results show this CMOS sensor is well-suited as a g- and X-ray detector with sensitivity at the few to 100 ppb level for 210Pb in a sample.

Multimodal Luminescent Yb3+ /Er3+ /Bi3+ -Doped Perovskite Single Crystals for X-ray Detection and Anti-Counterfeiting

Anti-counterfeiting techniques have become a global topic since they is correlated to the information and data safety, in which multimodal luminescence is one of the most desirable candidates for practical applications. However, it is a long-standing challenge to actualize robust multimodal luminescence with high thermal stability and humid resistance. Conventionally, the multimodal luminescence is usually achieved by the combination of upconversion and downshifting luminescence, which only responds to the electromagnetic waves in a limited range. Herein, the Yb³⁺ /Er³⁺ /Bi³⁺ co-doped Cs₂ Ag_0.6 Na_0.4 InCl₆ perovskite material is reported as an efficient multimodal luminescence material. Beyond the excitation of ultraviolet light and near-infrared laser (980 nm), this work extends multimodal luminescence to the excitation of X-ray. Besides the flexible excitation sources, this material also shows the exceptional luminescence performance, in which the X-ray detection limit reaches the level of nGy s^-1 , indicating a great potential for further application as a colorless pigment in the anti-counterfeiting field. More importantly, the obtained double perovskite features high stability against both humidity and temperature up to 400 °C. This integrated multifunctional luminescent material provides a new directional solution for the development of multifunctional optical materials and devices.

Perovskite Photodetectors Based on p-i-n Junction With Epitaxial Electron-Blocking Layers

Organic-inorganic hybrid perovskite single crystals (PSCs) have been emerged as remarkable materials for some optoelectronic applications such as solid-state photodetectors, solar cells and light emitting diodes due to their excellent optoelectronic properties. To decrease the dark current, function layers based on spin-coating method are frequently requested for intrinsic PSCs to block the injected current by forming energy barrier. However, the amorphous function layers suffer from small carrier mobility and high traps density, which limit the speed of the photoelectric response of perovskite devices. This work supposes to grow thick MAPbBr₃ and MAPbI₃ mono-crystalline thin films on the surface of intrinsic MAPbBr_2.5Cl_0.5 PSCs substrate by a heteroepitaxial growth technique to act as electron-blocking layers. Meanwhile, C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) layers are deposited on the opposite surface of substrate PSCs by spin-coating method to block injected holes. This Au-MAPbI₃-MAPbBr₃-MAPbBr_2.5Cl_0.5PSCs-C60-PCBM-Ag heterostructure can be used as excellent X-ray photodetector (XPD) due to its low dark current density of 6.97 × 10^-11 A cm^-2 at -0.5 V bias, high responsivity of 870 mA/W at -100 V bias and X-ray sensitivity as high as 59.7 μC mGy^-1 cm^-2 at -50 V bias.

Centimeter-Sized Single Crystal of Two-Dimensional Halide Perovskites Incorporating Straight-Chain Symmetric Diammonium Ion for X-Ray Detection

Two-dimensional (2D) AA'_n-1 M_n X_3n+1 type halide perovskites incorporating straight-chain symmetric diammonium cations define a new type of structure, but their optoelectronic properties are largely unexplored. Reported here is the synthesis of a centimeter-sized AA'_n-1 M_n X_3n+1 type perovskite, BDAPbI₄ (BDA=NH₃ C₄ H₈ NH₃ ), single crystal and its charge-transport properties under X-ray excitation. The crystal shows a staggered configuration of the [PbI₆ ]^4- layers, a band gap of 2.37 eV, and a low trap density of 3.1×10⁹  cm^-3 . The single-crystal X-ray detector exhibits an excellent sensitivity of 242 μC Gy_air ^-1  cm^-2 under the 10 V bias (0.31 V μm^-1 ), a detection limit as low as 430 nGy_air  s^-1 , ultrastable response current, a stable baseline with the lowest dark current drift of 6.06×10^-9  nA cm^-1  s^-1  V^-1 , and rapid response time of τ_rise =7.3 ms and τ_fall =22.5 ms. These crystals are promising candidates for the next generation of optoelectronic devices.

Photophysical Pathways in Highly Sensitive Cs2 AgBiBr6 Double-Perovskite Single-Crystal X-Ray Detectors

The sensitive detection of X-rays embodies an important research area, being motivated by a common desire to minimize the radiation doses required for detection. Among metal halide perovskites, the double-perovskite Cs₂ AgBiBr₆ system has emerged as a promising candidate for the detection of X-rays, capable of high X-ray stability and sensitivity (105 μC Gy^-1 cm^-2 ). Herein, the important photophysical pathways in single-crystal Cs₂ AgBiBr₆ are detailed at both room (RT) and liquid-nitrogen (LN₂ T) temperatures, with emphasis made toward understanding the carrier dynamics that influence X-ray sensitivity. This study draws upon several optical probes and an RT excitation model is developed which is far from optimal, being plagued by a large trap density and fast free-carrier recombination pathways. Substantially improved operating conditions are revealed at 77 K, with a long fundamental carrier lifetime (>1.5 µs) and a marked depopulation of parasitic recombination pathways. The temperature dependence of a single-crystal Cs₂ AgBiBr₆ X-ray detecting device is characterized and a strong and monotonic enhancement to the X-ray sensitivity upon cooling is demonstrated, moving from 316 μC Gy^-1 cm^-2 at RT to 988 μC Gy^-1 cm^-2 near LN₂ T. It is concluded that even modest cooling-via a Peltier device-will facilitate a substantial enhancement in device performance, ultimately lowering the radiation doses required.