Efficient Trap-Mediated Mn2+ Dopant Emission in Two Dimensional Single-Layered Perovskite (CH3CH2NH3)2PbBr4

In this work, Mn2+ has been efficiently and homogeneously doped into two-dimensional (2D) distorted single-layered EA2PbBr4 (EA: ethylammonium) via a reprecipitation method. Both the doped and undoped 2D layered lead halide perovskites (LHPs) were characterized using a combination of X-ray, electron microscopy, and spectroscopy techniques. The Mn2+-doped EA2PbBr4 (EA2PbBr4:Mn2+) shows a 78% photoluminescence (PL) quantum yield (QY) with complete quenching of self-trapped exciton emission because of efficient exciton trapping by defects created by dopants and small activation energy (∼9.8 meV) between the defect states and Mn2+ d states. Compared to the long lifetime (∼1.5 ms) of Mn2+ emission in CsPbCl3, the lifetime in 2D EA2PbBr4 is found to be ∼0.75 ms, resulting from the heavy atom effect. Additionally, the PL QY of Mn2+ emission can be further increased by codoping Zn2+ or Cd2+, which is attributed to a high density of trap states created by codoping, facilitating exciton to Mn2+ energy transfer. These results reveal the key role of trap states in the energy transfer of Mn2+-doped 2D LHPs.