Temperature-Induced Reversible Fluorescence Discoloration of Cs₃Cu₂Br₅ and Its Application in X-ray Imaging

As a promising new type of X-ray scintillator, lead-free metal halide materials have attracted extensive attention in recent years. Here, a blue emitter Cs3Cu2Br5 is successfully synthesized by simply mixing CsBr aqueous solution and CuBr acid solution. Due to the self-trapped excitons emission, it has a large Stokes shift and negligible self-absorption. The light yield of Cs3Cu2Br5 powder is calculated for the first time to be 22,000 ± 4000 photons/MeV. By using a new type of ultraviolet curable adhesive, the prepared Cs3Cu2Br5@UV films exhibit a high spatial resolution of 2.7 lp mm–1 in X-ray imaging, making it a promising candidate for high spatial X-ray imaging detectors. The prepared scintillator powder can change color at low temperatures (under 254 nm UV lamp), and photoluminescence emissions are 460 nm@300 K and 595 nm@240 K. The temperature-induced reversible fluorescence discoloration phenomenon of Cs3Cu2Br5 is speculated to be due to the decrease of energy level degeneracy. Additionally, owing to the distinctive property of exhibiting noticeable color changes in response to temperature variations, Cs3Cu2Br5 has the potential to become a thermochromic fluorescence material.