Self-trapped exciton assisted energy transfer from the band edge to Mn dopant in Mn²⁺-doped 2D organometal halide perovskites

Organo-metal halide perovskites (OMHPs) are relatively new entrants in the arena of doping as a means of tuning semiconductor functionalities, although initial efforts have demonstrated improved quantum yield and broadband emission in Mn-doped OMHPs. We investigated Mn²⁺ doped ethyl-ammonium lead bromide (EA₂PbBr₄:Mn²⁺), a two Dimensional OMPH, using low-temperature optical spectroscopy techniques. Our results show that while for temperatures T > 120 K, photoluminescence (PL) is dominated by emission from Mn²⁺, with complete suppression of band-edge (BE) emission. For T < 120 K, in addition to BE emission, PL is observed from self-trapped excitons (STEs). While establishing that STEs form the most dominant route in energy transfer from the BE to Mn²⁺ dopants for 20 K < T < 120 K, using spin-polarized spectroscopy we further demonstrate strong exchange coupling between the quantum confined host carriers and dopant ions.