Dual-emissive luminescence in OIHMH single crystals: tunable red-green emissions via Mn2+ doping and theoretical insights

The burgeoning demand for materials with tunable photoluminescence properties for applications has necessitated the exploration of novel luminescent materials. This study presents the synthesis and characterization of a novel 0D organic–inorganic hybrid metal halide (OIHMH) single crystal, C6H14N2CdBr4, which exhibits intriguing luminescent properties upon Mn2+ doping. The introduction of single Mn2+ ions results in a dual-emission, with the unexpected emergence of a red emission peak at 627 nm, in addition to the conventional tetrahedral green emission at 525 nm. This dual-emission is attributed to the distinct inter-tetrahedral distances within the crystal structure of C6H14N2CdBr4 with varying distances between [CdBr4]2− tetrahedra, influencing the spatial distribution and interaction of the [MnBr4]2− tetrahedra. Electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations reveal the 627 nm and 525 nm emissions are attributed to the d–d transition of magnetic coupled Mn2+–Mn2+ pairs and isolated Mn2+ ions, respectively. This study not only advances the understanding of the luminescence mechanisms of Mn2+ but also paves the way for the development of tunable luminescent materials.