Near-unity and narrow green emission from a manganese(ii) bromide for efficient WLEDs and 3D X-ray imaging.

Developing efficient, narrow-band, and environmentally friendly emitters is crucial for advanced optoelectronics. Herein, we report a zero-dimensional (0D) organic-inorganic hybrid manganese(ii) halide, (TPS)2MnBr4 (TPS = triphenylsulfonium), engineered via cation selection. This material simultaneously achieves near-unity photoluminescence quantum yield (PLQY ≈ 99.6%) and exceptionally narrow green emission (FWHM = 40 nm) for a Mn2+ emitter. Structural analysis and theoretical calculations reveal that the rigid TPS+ cation induces a specific crystal packing that minimizes [MnBr4]2- tetrahedral distortion through weaker hydrogen bonding interactions. This structural optimization leads to suppressed electron-phonon coupling, explaining the narrow bandwidth while maintaining high efficiency. These outstanding properties enable high-performance white light-emitting diodes (WLEDs) and 3D X-ray Imaging. This work demonstrated targeted cation engineering as a powerful strategy to overcome intrinsic Mn2+ limitations and presents a high-performance, eco-friendly material for multifunctional optoelectronic applications.