Organic-inorganic hybrid manganese bromine single crystal with dual-band photoluminescence from polaronic and bipolaronic excitons

Organic molecule incorporation into inorganic halide brings up a series of variable optical physics and applications. Here, we report a new zero-dimensional Mn-based hybrid metal halide of C4H14N2MnBr4 single crystals by using bi-amine group organic ions incorporation, which shows bright orange emission at room temperature. Interestingly, it exhibits unique dual-emission bands at 516 nm and 623 nm, both bands are related to the polaronic exciton or selftrapped exciton(STE1) and the bipolaronic exciton(STE2) due to the enhanced charged electron-phonon coupling by the incorporation of bi-amine-group molecular ions in the manganese halide lattice, which are also combined with the d-d transition of single Mn and Mn pair at a Mn-Mn distance close to a critical number of about 6.6 Å. This distance is found to be the critical distance between Mn ions for their paramagnetic and pair ferromagnetic phases in the manganese halides. The temperature-dependent photoluminescence (PL) spectra show that the C4H14N2MnBr4 single crystals have a sensitive reversible thermo-induced PL characteristic, i.e., its orange and green PL colors can be converted back and forth through the temperature dependent electron-phonon coupling coefficient variations, during which there are different phase transitions.