Fluorinated Benzyltriphenylphosphonium Manganese-Halide Scintillators for High-Performance Underwater X-ray Imaging

Manganese(II)-based organic-inorganic metal halides have emerged as promising candidates for the next generation of high-performance scintillators due to their environmental friendliness. However, their practical application is hindered by poor stability, especially in humid or aqueous environments. In this study, we designed a series of fluorinated benzyltriphenylphosphonium salts by varying the number and position of fluorine atoms on the benzyl group. Using these salts as organic cations, four manganese(II) organic-inorganic metal halides─(BzTPP)₂MnBr₄, (FBzTPP)₂MnBr₄, (3,4-2FTPP)₂MnBr₄, and (3,4,5-3FTPP)₂MnBr₄─were synthesized. Among them, (FBzTPP)₂MnBr₄ exhibited the highest photoluminescence quantum yield (PLQY = 99.74%) and photon yield (63,000 photons MeV^-1), with a detection limit as low as 83.6 nGy s^-1. When combined with PVDF to form flexible films for X-ray imaging, a spatial resolution of 7.15 lp mm^-1 was achieved. Notably, fluorine substitution significantly improved the water stability of both crystals and films, enabling clear underwater X-ray imaging. This study demonstrates an effective approach to enhancing the stability and performance of Mn-based scintillators through tailored organic cation design.