Dynamic and Underwater X‐ray Imaging Enabled by Instant Ion Exchange of Copper Halide Scintillators

ABSTRACT Organic–inorganic hybrid copper halides, with exceptional optoelectronic properties encoded in their highly tunable crystal structure, are emerging as promising candidates for next‐generation scintillators. However, achieving both high light yield and fast luminescence decay in copper halides remains a significant challenge, limiting their application in real‐time X‐ray imaging. Here, a simple yet effective ion exchange approach is developed to enable rapid conversion of (MeEn) 2 Cu 4 Br 6 (MeEn = 3‐methylbut‐2‐enyl(triphenyl)phosphanium) to (MeEn) 2 Cu 4 I 6 , resulting in a near‐unity photoluminescence quantum yield (PLQY), a 1.7‐fold increase in light yield (39700 photons MeV −1 ), and a 15‐fold reduction in luminescence decay time (2.4 µs). Mechanistic investigations reveal that the enhanced scintillation properties arise from reduced lattice distortion, appropriately weakened electron‐phonon coupling, and strong spin–orbit coupling induced by the heavy iodine atom. Beyond (MeEn) 2 Cu 4 X 6 , this approach is applicable to a variety of copper halides, leading to consistent improvements in photophysical performance. Finally, by embedding (MeEn) 2 Cu 4 I 6 with a polymer matrix, the resulting scintillation film is further entailed with desired flexibility and water resistance, demonstrating its capability in static, dynamic, curved, and underwater X‐ray imaging.