Liquid-based cationic ligand engineering in one-dimensional bismuth bromide perovskites: A-site influence on scintillation properties

Abstract

Low-dimensional bismuth-based hybrid organic–inorganic halide perovskites (Bi-HOIPs) are intriguing scintillating materials due to their anisotropic nature. However, a systematic investigation on Bi-HOIP frameworks for X-ray detection imaging remains lacking. In this work, we present the diverse X-ray detection responses in a series of Bi-HOIPs that are incorporated into a polydimethylsiloxane (PDMS) matrix utilizing ionic liquids (ILs) as organic ligands, namely, 1-butyl-1-methyl-pyrrolidinium (BMP), 1-(3-aminopropyl)imidazole (API), and 1-butyl-3-methyl-imidazolium (BMI). The as-synthesized Bi-HOIPs in this series exhibited a modest light yield of ∼1000 photons per keV at room temperature. Interestingly, the incorporation of tin (Sn), instead of bismuth, resulted in radioluminescence intensity enhancement at low temperatures. An abrupt thermal quenching occurred in the case of APISnBiBr₅ and APISn₂Br₁₀, leading to an absence of light yield at RT. Interestingly, thermoluminescence (TL) measurements showed that the glow curve was absent in BMIBiBr₄ and APIBiBr₅, demonstrating the weak contribution of a defect within the crystal lattices. On the contrary, BMPBiBr₄, APISnBiBr₅ and APISn₂Br₁₀ displayed glow curves at temperatures above 100 K. We believe that controlling the number of defects promoted tunable modest distribution traps, manifesting their light yield profile. In terms of the decay profile, BMIBiBr₄ exhibited a fast decay component of 4 ns, while APIBiBr₅ and BMPBiBr₄ yielded a fast decay of 6 ns. A distinct constituent within the ILs could serve as a tuning factor, thereby generating different optical responses and scintillation features. We postulate that this can be attributed to the band gap and polaron signature in BMIBiBr₄, which manifested a faster quenching rate than BMPBiBr₄ and APIBiBr₅. This work sheds new insights on how the population of direct manipulation traps in IL-based bismuth halide perovskites can be driven by regulating the number of halogens at the X-sites of the targeted compounds.