Halogen‐Regulated Luminescent Silver(I) Halide Complexes and the Gel Scintillation Screen for X‐Ray Imaging

ABSTRACT Metal halide scintillators have attracted continuously increasing interest for low‐dose and high‐resolution X‐ray imaging, yet typical luminescent silver halides suffer from severe hygroscopicity and exciton quenching caused by Ag–Ag cluster aggregation. To address these challenges, we design and report mononuclear five‐coordinate silver(I) halide complexes (dppb) 2 AgX·DMSO (X = I, Br, Cl) with 1,2‐Bis(diphenylphosphino)benzene (dppb) ligand. Halogen substitution enables tunable broadband emission, while the chloride analogue achieves efficient thermally activated delayed fluorescence (TADF) and a high PLQY of 76%. The chloride analogue possesses more rigid AgClP 4 coordination environment compared with its bromide and iodide counterparts, enabling restricts excited‐state relaxation, suppresses non‐radiative decay, and preserves favorable singlet‐triplet energetics and spin‐orbit coupling. Meanwhile, the chloride analogue shows superior scintillation with a high light yield of 26631 photons/MeV, and a detection limit of 304.67 nGy air s −1 . Furthermore, a high spatial resolution of 20.2 lp mm −1 for X‐ray imaging is achieved based on the transparent Ag‐Cl composite gel scintillator screen. This work not only provides a promising design principle for achieving high scintillation in TADF‐type Ag(I) halide complexes by halogen regulation, but also provide a new platform for Ag(I) halide complexes in X‐ray imaging.