Bismuth-Assisted Synthesis of Low-Dimensional Copper Halide for X-ray Imaging Scintillators

Lead-free perovskite-related materials are gaining significant attention as X-ray scintillators due to their low toxicity and high X-ray absorption cross section, which leads to a high light yield. The zero-dimensional copper halide Cs 3 Cu 2 I 5 (CCI) exhibits a very high photoluminescence quantum yield and blue emission, making it compatible with photomultipliers with a higher photon detection efficiency in this wavelength range. However, the oxidation of copper, along with the phase transition to a less emissive one-dimensional copper halide, presents significant stability challenges for these powerful scintillation materials, ultimately limiting their potential for future commercialization. In this work, we propose heavy atom doping with bismuth, which not only enhances the oxidation resistance of copper but also inhibits the phase transformation. By addition of trivalent bismuth during the antisolvent synthesis, we achieved nearly 60% increase in radioluminescence and a spatial resolution of 19 lp/mm while maintaining the original blue emission. We also compared the scintillation properties of our CCI:Bi with those of commercial LYSO:Ce, both of which emit at a peak wavelength of 450 nm. By irradiating the materials at varying dose rates, we evaluated their sensitivity to changes in irradiation. LYSO:Ce generates 33,000 photons/MeV, while our CCI:Bi produces over 66,000 photons/MeV, based on radioluminescence area comparisons. Furthermore, the calculated detection limits are 46 nGy/s for CCI:Bi─over 100 times lower than the standard dose for medical examinations─and 95 nGy/s for LYSO:Ce. These findings underscore the significant potential of CCI:Bi as a highly sensitive and stable X-ray scintillator.