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.