Ionic Ag(I) Complexes Exhibiting Very Fast Reverse Intersystem Crossing for X‐Ray Imaging

Organic complex‐based materials show promise for replacing inorganic scintillators due to their low cost, mild synthesis and ease of processing into large‐area films. Specifically, ionic Ag(I) complexes offer both heavy‐atom‐enhanced x‐ray absorption and good solubility, enabling highly doped, transparent films ideal for high‐resolution x‐ray imaging. Yet, their development has been limited because silver's high oxidation potential impedes triplet exciton harvesting—a critical yet challenging process during x‐ray conversion where secondary electrons generate abundant triplet states. Here, we present a design strategy for metal‐to‐ligand charge‐transfer Ag(I) complexes exhibiting thermally activated delayed fluorescence (TADF) and report a series of ionic Ag(I)‐based scintillators. These materials achieve high reverse intersystem crossing rates (>10 7 s −1 ) and microsecond‐scale decay lifetimes, enabling efficient triplet exciton harvesting during radioluminescence and light yields up to 53797 photons/MeV. Transparent films fabricated from these complexes demonstrate excellent x‐ray imaging performance with a spatial resolution of 86.7 lp/mm. This work offers new design principles for coordination‐compound scintillators and advances high‐performance scintillation technology.