Phenyl Substitution in Neutral Manganese(II) Bromide Glass Scintillators for X-ray Imaging

Manganese halides have attracted a considerable amount of interest for their inherent nontoxicity, diverse single-crystal polymorphism, and tunable photoluminescence. Nevertheless, achieving high glass-forming ability (GFA) together with efficient radioluminescence in manganese(II) halide systems remains challenging. In this work, a phenyl-substitution strategy was developed to fabricate neutral manganese(II) bromide glass scintillators. By progressively replacing aliphatic cyclohexyl (Cy-) groups with aromatic phenyl (Ph-) moieties on phosphine oxide ligands, we rationally designed three zero-dimensional MnBr2(L)2 complexes (L = Cy3PO, CyPh2PO, and Ph3PO). Notably, substituting Cy- groups with Ph- moieties alters the molecular rigidity and thus the glass transition temperature. Among the obtained glasses, the MnBr2(Ph3PO)2-based system displays the best GFA with a Tg/Tm ratio of 0.71, alongside the lowest melting point (Tm = 233 °C) and highest glass transition temperature (Tg = 85 °C). The corresponding glass scintillator demonstrates a light yield of 8170 photons MeV–1, optical transmittance exceeding 85% in the visible range (500–780 nm), and a spatial resolution up to 14.5 lp mm–1 in X-ray imaging. This work highlights that phenyl substitution facilitates halide vitrification and improves scintillation performance, suppresses intrinsic crystallization of neutral phosphine oxide manganese(II) halide glasses, and offers a viable route for high-performance manganese(II) halide scintillators.