Metal Ion Doping in Cs ₃ Cu ₂ I ₅ Crystals: Strategies to Regulate the Optoelectronic Property for Enhanced X‐Ray Scintillation and Imaging

The advancement of scintillators is of pivotal significance in X‐ray detection and imaging technologies, with widespread applications spanning security inspection, manufacturing quality control, medical diagnostics, and frontier scientific instruments. In recent years, metal halide perovskites and their derivatives have attracted considerable research interest as promising scintillators, attributed to their superior optoelectronic properties. Notably, zero‐dimensional (0D) copper halide Cs ₃ Cu ₂ I ₅ crystals have emerged as a promising candidate for next‐generation scintillation materials, owing to their near‐unity quantum yield, facile synthesis process, and excellent stability against humidity and X‐ray irradiation. This review first summarizes the crystalline structure of Cs ₃ Cu ₂ I ₅ and its two intrinsic emission mechanisms. Subsequently, it discusses the progress in X‐ray scintillation imaging performance of Cs ₃ Cu ₂ I ₅ ‐based nanocrystals and single crystals. The review then elaborates on the underlying mechanisms of metal ion doping (including Tl ⁺ , In ⁺ , Mn ²⁺ , alkali metals, and alkaline earth metals) in tailoring the optoelectronic properties of Cs ₃ Cu ₂ I ₅ crystals for scintillation applications. Finally, it highlights the emerging application prospects of Cs ₃ Cu ₂ I ₅ crystals, such as dual‐energy X‐ray imaging, multi‐energy X‐ray linear‐array detectors, and computed tomography imaging.