Thermally Activated Delayed Fluorescent Ag(I) Complexes for Highly Efficient Scintillation and High-Resolution X-Ray Imaging

Organic thermally activated delayed fluorescent (TADF) scintillators hold promising potential for applications in medical radiography and security detection, but the poor X-ray absorption ability and inferior radioluminescence (RL) hampered their progression. Herein, the study has pioneered the development of high-performance TADF Ag(I)-based scintillators from M2X2(dppb)2 (M = Ag, Cu; X = Cl, Br, I) complexes with 1,2-Bis(diphenylphosphino)benzene (dppb) ligand. In comparison with Cu(I) complexes, the Ag(I) series generally exhibited superior scintillation performance. Notably, Ag2Cl2(dppb)2 (Ag1) stands out with exceptionally high RL intensity (approximate to 125% higher than that of CsI:Tl) and a low detection limit of 59.8 nGy s-1. The outstanding scintillation performance of Ag1 is primarily attributed to the synergistic effect of the high exciton utilization efficiency origin from a small singlet-triplet energy gap, enhanced X-ray absorption capacity by heavy atoms, and the high photoluminescence quantum yield (76.47% in ambient atmosphere). By fabricating a flexible film constructed with Ag1 submicron crystalline powders, a high spatial resolution of 25.0 lp mm-1 for X-ray imaging is obtained. It offers new opportunities for utilizing TADF metal-organic complexes for highly efficient X-ray scintillation and imaging. Scintillators with good radioluminescence performance are prepared by combining the TADF mechanism to optimize the utilization of triplet excitons, coupled with increased X-ray absorption through heavy atoms, verifying the advantages of Ag(I)-halide complexes on radioluminescence. Besides, the influence of halogens on photoluminescence and radioluminescence are investigated. As a practical application, Ag2Cl2(dppb)2 is applied to fabricate flexible scintillator films, achieving high-resolution imaging of 25 lp mm-1. image