Pressure-induced tunable luminescence of Mn2+–Mn2+ dimers in Mn-based metal halides (C6H9N2)2MnBr4

The super-exchange coupled Mn2+–Mn2+ dimer can be formed by doping high concentrations of Mn2+ ions. However, since the distribution of Mn2+ ions strongly depends on the crystal structure of the host lattice, the tuning of Mn2+ ion related emission properties remains limited. Here, a pressure-treated strategy is reported to induce a new red emission band of Mn2+–Mn2+ dimers in the Mn-based metal halide (C6H9N2)2MnBr4. The red and green emission bands generated by Mn2+–Mn2+ dimers and isolated Mn2+ ions exhibit different emission behaviors under pressure. Notably, the emission of the Mn2+–Mn2+ dimer exhibits a wide tunability range from 660 to 770 nm, which is attributed to the increased crystal field splitting energy resulting from the reduced Mn–Br bond length under pressure. Our findings highlight the important role of Mn2+–Mn2+ dimers in pressure-tuned optoelectronic properties and provide guidance for the design of novel optoelectronic devices with desired emission characteristics.