Physical Properties of Candidate X-ray Detector Material Rb₄Ag₂BiBr₉

Abstract

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 lowtemperature 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 Rb 4 Ag 2 BiBr 9 , which has been identified as a potential candidate for X-ray radiation detection applications. The measured heat capacity for Rb 4 Ag 2 BiBr 9 implies that there are no structural phase transitions upon cooling. Temperature dependence of thermal transport measurements further suggests remarkably low thermal conductivities of Rb 4 Ag 2 BiBr 9 that are comparable to the lowest reported in literature. The bulk crystal resistivity is determined to be 2.59 × 10 9 Ω•cm from the current−voltage (I−V) curve. Density of trap states is estimated to be ∼10 10 cm −3 using the space-charge-limited-current measurements. The fabricated Rb 4 Ag 2 BiBr 9 -based X-ray detector shows good operational stability with no apparent current drift, which may be ascribed to the 2D crystal structure of Rb 4 Ag 2 BiBr 9 . Finally, by varying the X-ray tube current to change the corresponding dose rate, the Rb 4 Ag 2 BiBr 9 X-ray detector sensitivity is determined to be 222.03 μC Gy −1 cm −2 (at an electric field of E = 24 V/mm).

Crystal growth, structural and electronic characterizations of zero-dimensional metal halide (TEP)InBr4 single crystals for X-ray detection

“…The thermal conductivity was determined to be between 0.33 ± 0.05 and 0.45 ± 0.07 W m −1 K −1 , while the specific heat for (TEP)InBr 4 is between 682 and 909 J kg −1 K −1 ). The obtained low thermal conductivity here for (TEP)InBr 4 is consistent with the results for other low-dimensional metal halides, including 0.1 W m −1 K −1 for 2D Rb 4 Ag 2 BiBr 9 , 28 0.11 W m −1 K −1 for 2D hybrid perovskite BA 2 MA 3 Pb 4 I 13 (BA = butylammonium), 29 and <0.1 W m −1 K −1 for 0D Cs 3 Cu 2 I 5 . 30 Based on these results, potential practical applications of (TEP)InBr 4 would need addressing its air sensitivity ( e.g.…”

High Ionic Conduction and Polarity-Induced Piezoresponse in Layered Bimetallic Rb4Ag2BiBr9 Single Crystals

“…From the reflectance data, the Kubelka–Munk function, which is defined as [ F false( R false) ] = false( 1 − R false) 2 2 R is determined, where R is the reflectance from the samples at each wavelength. F ( R ) is plotted against the incident photon energy h ν (Figure S5 in the Supporting Information), showing two distinct absorption features at 2.69 and 3.25 eV, which also match well with earlier reports. , The absorption peak at 2.69 eV has been attributed to the excitonic absorption and that at 3.25 eV to the higher conduction band transitions . These values are also in the same range as reported for other bismuth-silver halide double perovskites. , The Tauc plot, shown in Figure , plotted between [ F ( R ) h ν] 1/η versus h ν, estimates a band gap of 2.43 eV considering direct (η = 1/2) band transition …”

“…F(R) is plotted against the incident photon energy hν (Figure S5 in the Supporting Information), showing two distinct absorption features at 2.69 and 3.25 eV, which also match well with earlier reports. 36,40 The absorption peak at 2.69 eV has been attributed to the excitonic absorption and that at 3.25 eV to the higher conduction band transitions. 36 These values are also in the same range as reported for other bismuth-silver halide double perovskites.…”

Zero-Dimensional Zinc Halide Organic Hybrids with Excellent Optical Waveguide Properties

“…Organic metal halide hybrids (OMHHs) have aroused interest in the creation of novel X-ray detectors, light-emitting diodes, and photodetectors, ,− owing to their unprecedented structural flexibility, exceptional band gap tunability, and efficient luminescence. − By selecting a suitable organic cation and a metal halide anion, diverse structures ranging from three-dimensional (3D) to zero-dimensional (0D) can be produced at the molecular level. − Among them, 0D materials are candidate materials for solid-state phosphors due to their low self-absorption and high quantum yield . In principle, the solution-treated OMHHs can also be used as an ideal model for optical waveguide materials for the following reasons: (1) these materials have simpler synthesis conditions and good stability; (2) their high crystallinity is conductive to reduce the optical loss; (3) the compositions of OMHHs help to tune the optical emissions; and (4) these materials can be manufactured into nanowires, , nanocrystals, − and nanorods by simple, solution-processable methods, enabling their integration into miniaturized devices .…”