Physical Properties of Candidate X‑ray Detector Material Rb₄Ag₂BiBr₉

Recently, metal halide perovskites have emerged as promising semiconductor candidates for sensitive X-ray photon detection due to their suitable band gap energies, excellent charge transport properties, and low material cost afforded by their low-temperature solution-processing preparation. Here, we report an improved methodology for single crystal growth and thermal and electrical properties of a two-dimensional (2D) layered halide material Rb4Ag2BiBr9, which has been identified as a potential candidate for X-ray radiation detection applications. The measured heat capacity for Rb4Ag2BiBr9 implies that there are no structural phase transitions upon cooling. Temperature dependence of thermal transport measurements further suggests remarkably low thermal conductivities of Rb4Ag2BiBr9 that are comparable to the lowest reported in literature. The bulk crystal resistivity is determined to be 2.59 × 109 Ω·cm from the current–voltage (I–V) curve. Density of trap states is estimated to be ∼1010 cm–3 using the space-charge-limited-current measurements. The fabricated Rb4Ag2BiBr9-based X-ray detector shows good operational stability with no apparent current drift, which may be ascribed to the 2D crystal structure of Rb4Ag2BiBr9. Finally, by varying the X-ray tube current to change the corresponding dose rate, the Rb4Ag2BiBr9 X-ray detector sensitivity is determined to be 222.03 μC Gy–1 cm–2 (at an electric field of E = 24 V/mm)

Synthesis and Characterization of New Hybrid Organic–Inorganic Metal Halides [(CH₃)₃SO]M₂I₃ (M = Cu and Ag)

Recently, all-inorganic copper(I) metal halides have emerged as promising optical materials due to their high light emission efficiencies. This work details the crystal structure of the two hybrid organic–inorganic metal halides [(CH3)3SO]M2I3 (M = Cu and Ag) and their alloyed derivatives [(CH3)3SO]Cu2–xAgxI3 (x = 0.2; 1.25), which were obtained by incorporating trimethylsulfoxonium organic cation (CH3)3SO+ in place of Cs+ in the yellow-emitting all-inorganic CsCu2I3. These compounds are isostructural and centrosymmetric with the space group Pnma, featuring one-dimensional edge-sharing [M2I3]− anionic double chains separated by rows of (CH3)3SO+ cations. Based on density functional theory calculations, the highest occupied molecular orbitals (HOMOs) of [(CH3)3SO]M2I3 (M = Cu and Ag) are dominated by the Cu or Ag d and I p orbitals, while the lowest unoccupied molecular orbitals (LUMOs) are Cu or Ag s and I p orbitals. [(CH3)3SO]Cu2I3 single crystals exhibit a semiconductor resistivity of 9.94 × 109 Ω·cm. Furthermore, a prototype [(CH3)3SO]Cu2I3 single-crystal-based X-ray detector with a detection sensitivity of 200.54 uCGy–1 cm–2 (at electrical field E = 41.67 V/mm) was fabricated, indicating the potential use of [(CH3)3SO]Cu2I3 for radiation detection applications

Investigation of the Solution Chemistry of Hybrid Organic–Inorganic Indium Halides for New Material Discovery

Recently, metal halide perovskites (MHPs) have emerged as a new class of materials for optical and electronic applications such as solar cells and ionizing radiation detectors. Although the solution-processability of MHPs is among their greatest advantages, the solution chemistries of most metal halide systems and their relationship with the observed structural and chemical diversity are poorly understood. In this work, we study the solution chemistry of a model indium halide system, methylammonium (MA)–In–Br, using a combination of the UV–vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS) measurements, small-angle X-ray scattering (SAXS), and density functional theory (DFT) calculations. Our results show that indium could form either octahedral [InBr63–] or tetrahedral [InBr4–] anions in solution or a combination of both, depending on the loading ratios of MABr and InBr3 reactants. Understanding the solution chemistry of this system and recognizing the optical fingerprints of these polyanions allow for targeted crystallization of two novel compounds: MAInBr4 featuring tetrahedral [InBr4–] anions and MA2InBr5 containing both octahedral [InBr63–] and tetrahedral [InBr4–] anions. Further increase of the MABr content leads to the formation of previously reported MA4InBr7, containing only octahedral [InBr63–] anions separated by Br– anions. Our results suggest that understanding the solution chemistry of multinary metal halide systems could be a valuable tool for discovering functional materials for practical applications

Zero-Dimensional Broadband Yellow Light Emitter (TMS)₃Cu₂I₅ for Latent Fingerprint Detection and Solid-State Lighting

We report a new hybrid organic-inorganic Cu(I) halide, (TMS)3Cu2I5 (TMS = trimethylsulfonium), which demonstrates high efficiency and stable yellow light emission with a photoluminescence quantum yield (PLQY) over 25%. The zero-dimensional crystal structure of the compound is comprised of isolated face-sharing photoactive [Cu2I5]3– tetrahedral dimers surrounded by TMS+ cations. This promotes strong quantum confinement and electron-phonon coupling, leading to a highly efficient emission from self-trapped excitons. The hybrid structure ensures prolonged stability and nonblue emission compared to unstable blue emission from all-inorganic copper(I) halides. Substitution of Cu with Ag leads to (TMS)AgI2, which has a one-dimensional chain structure made of edge-sharing tetrahedra, with weak light emission properties. Improved stability and highly efficient yellow emission of (TMS)3Cu2I5 make it a candidate for practical applications. This has been demonstrated through utilization of (TMS)3Cu2I5 in white light-emitting diode with a high Color Rendering Index value of 82 and its use as a new luminescent agent for visualization of in-depth latent fingerprint features. This work illuminates a new direction in designing multifunctional nontoxic hybrid metal halides