Direct emission from quartet excited states triggered by upconversion phenomena in solid-phase synthesized fluorescent lead-free organic-inorganic hybrid compounds
We report, for the first time, solid-phase gram-scale syntheses of two lead-free, zero-dimensional (0D) fluorescent organic-inorganic hybrid compounds, [Bu4N]2[MnBr4] (1) and [Ph4P]2[MnBr4] (2) achieved by grinding the organic and inorganic precursor salts. Solid-phase synthetic route has several advantages for modulating molecular dimensionalities. During grinding, organic cations and Mn2+ cations are co-crystallized together in solid-state, forming 0D assembly at the molecular level where each individual metal centers are surrounded by organic cations. Green light emission peaked at 520 nm is observed with photoluminescence (PL) quantum yield (QY) of 47% for both compounds. Here, we also report, for the first time, the upconversion phenomenon which triggers different emission energies occurred in different quartet states of Mn, 4T1(4G), 4T2(4G), 4A1(4G), 4E(4G), 4T2(4D), 4E(4D), and 4T1(4P). These optical properties are unusual phenomena which breaks the Kasha’s rule of emission. Single particle imaging and low-temperature PL measurement are performed to get a deeper insight into these ground products. These results pave a new path to develop highly fluorescent non-toxic hybrid compounds with remarkable optical properties.