Zero‐Dimensional Cesium Copper Iodide: Synthesis and Applications in Ultraviolet and X‐Ray Detection and Imaging

Since the discovery of self‐trapped exciton (STE) emission in copper‐based halides in 2018, novel copper‐based metal halides have gained significant attention in optoelectronics due to their high absorption, tunable bandgap, and long carrier lifetime. Among them, Cs 3 Cu 2 I 5 stands out for its high light yield and notable STE luminescence mechanism. This review comprehensively summarizes the fundamental properties, synthesis strategies, and advanced applications of Cs 3 Cu 2 I 5 in ultraviolet (UV) and X‐ray detection and imaging. We elucidate the relationship between its zero‐dimensional crystal structure—composed of isolated [Cu 2 I 5 ] 3− clusters—and its exceptional optoelectronic performance, particularly the STE mechanism enabling efficient luminescence and detection. Subsequently, we systematically categorize and critically assess various synthesis methodologies, ranging from top‐down solid‐phase reactions to bottom‐up wet‐chemical and vapor‐phase depositions, discussing their respective impacts on tailoring material morphology, crystallinity, and device performance. The review highlights key achievements in high‐sensitivity solar‐blind UV photodetectors and low‐dose X‐ray detection using scintillators with high resolution. Finally, current challenges and future prospects for Cs 3 Cu 2 I 5 ‐based optoelectronic devices are outlined, providing a valuable reference for researchers in materials science and photonics.