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 Mn 2+ substitution into 2D layered perovskites (C 8 H 20 N 2 )PbBr 4 was investigated, demonstrating broad-band orange-red emission originating from the 4 T 1 → 6 A 1 transition of Mn 2+ dopant. The photoluminescence quantum yield (PLQY) of Mn 2+ emission is up to 60.8% related to the energy transfer in coupled states. We verify that an actual Mn 2+ dopant as low as 0.476% reaches a high PLQY, whereas the nominal adding amount is 0.8 as the Mn 2+ /Pb 2+ ratio. The small activation energy (∼6.72 meV) between the Mn 2+ d state and the trap state accounts for this highly efficient energy transfer and photoluminescence. The proposed luminescence mechanism in Mn 2+ -doped 2D halide perovskites would provide unique insights into the doping design toward high-performance luminescence materials.