H/F Substitution Regulates the Local Environment and Excited-State Relaxation of Tetrahedral Mn(II) Centers for Near-Unity Luminescence and X-ray Scintillation

Abstract Molecular-level regulation of isolated luminescent centers offers a promising route to efficient and flexible X-ray scintillators. Herein, we develop a hydrogen-to-fluorine (H/F) substitution strategy for tuning isolated Mn2+ emitters in a zero-dimensional hybrid chloride. The fluorinated analogue (FTEA)2MnCl4 (FTMC) is isostructural with the parent (TEA)2MnCl4 (TMC), while fluorination introduces F···Cl interactions (15.1%) and subtly modulates the local coordination environment of MnCl4 units. This molecular modification nearly doubles the photoluminescence quantum yield from 49.8% for TMC to 97.5% for FTMC, enabled by concurrent enhancement of radiative decay and suppression of nonradiative relaxation. Notably, FTMC further exhibits a high X-ray scintillation light yield of 78,400 photons MeV–1, an ultralow detection limit of 32.42 nGy s–1, and favorable operational stability. Moreover, a flexible FTMC@PDMS scintillator enables high-resolution X-ray imaging with a spatial resolution of 11.9 lp mm–1. This work establishes H/F substitution as an effective molecular strategy for regulating excited-state relaxation in isolated Mn2+ emitters and advancing high-performance flexible X-ray scintillators.