Metal‐Coordination‐Triggered Anti‐Kasha Phosphorescence for Efficient Triplet Exciton Utilization in X‐Ray Imaging

Scintillators have attracted considerable attention owing to their important applications in industrial inspection and medical X‐ray imaging. However, efficient harvesting of triplet excitons to achieve high radioluminescence (RL) efficiency remains highly challenging. Herein, we propose a metal‐coordination‐triggered strategy that activates anti‐Kasha phosphorescence, enabling triplet‐exciton‐dominated multiple radiative decay pathways that originate from both the lowest and second triplet states and the lowest singlet state. Coordination with Ag + effectively narrows the singlet–triplet energy gap and enhances spin–orbit coupling (SOC), thereby accelerating intersystem crossing (ISC) and facilitating radiative decay from higher‐lying triplet states. The resulting silver(I) complex exhibits pronounced anti‐Kasha phosphorescence and achieves a high photoluminescence quantum yield of up to 77.7% in PVP films. Multiple triplet radiative decay pathways and enhanced x‐ray absorption improve exciton harvesting efficiency, resulting in intensified radioluminescence. Together with the superior film quality of the silver(I) complex, this enables high‐resolution x‐ray imaging with a spatial resolution of 68.2 lp mm − 1 , far exceeding that of the ligand (16.6 lp mm − 1 ). These results demonstrate the critical role of metal‐fragment coordination in regulating excited‐state dynamics under x‐ray excitation and provide a new strategy for developing high‐performance anti‐Kasha phosphorescent scintillators with efficient triplet‐exciton utilization.