Unveiling Mn²⁺ Dopant States in Two-Dimensional Halide Perovskite toward Highly Efficient Photoluminescence

Doping is able to create novel optoelectronic properties of halide perovskites, and the involved mechanism of efficient emission is still a challenge. Herein Mn2+ substitution into 2D layered perovskites (C8H20N2)­PbBr4 was investigated, demonstrating broad-band orange-red emission originating from the 4T1 → 6A1 transition of Mn2+ dopant. The photoluminescence quantum yield (PLQY) of Mn2+ emission is up to 60.8% related to the energy transfer in coupled states. We verify that an actual Mn2+ dopant as low as 0.476% reaches a high PLQY, whereas the nominal adding amount is 0.8 as the Mn2+/Pb2+ ratio. The small activation energy (∼6.72 meV) between the Mn2+ d state and the trap state accounts for this highly efficient energy transfer and photoluminescence. The proposed luminescence mechanism in Mn2+-doped 2D halide perovskites would provide unique insights into the doping design toward high-performance luminescence materials.