Energy‐Transfer Pathways for Photoluminescence in Mn ²⁺ ‐Doped 2D Hybrid Lead Bromide Systems

ABSTRACT

Mn ²⁺ doping in hybrid perovskite‐derived two‐dimensional (2D) lead bromide systems exhibits efficient Mn ²⁺ emission and enhanced environmental stability compared to their 3D analogue perovskites. Here, we investigate the sensitization of Mn ²⁺ emission in doped 2D BA ₂ PbBr ₄ (BA = butylammonium) through comprehensive temperature‐dependent PL analyses. We establish a near‐resonant energy transfer from the host excitonic state to the higher‐lying Mn ²⁺ multiplet ( ⁴ T _2g (D)), followed by successive multiphonon‐assisted de‐excitations through the intermediate multiplets of Mn ²⁺ between the originally populated ⁴ T _2g (D) and the first excited multiplet, ⁴ T _1g (G) state. Infrared (IR) spectroscopy identifies the highest‐energy phonon mode at 59.2 meV in BA ₂ PbBr ₄ , more than twice that of the previously analyzed 3D perovskite CsPbCl ₃ nanocrystals, pointing to a significantly more efficient multiphonon relaxation and suppressed phonon bottleneck effects in the 2D case, explaining the efficient Mn ²⁺ emission observed even at low temperatures. The contrasting behaviors are further accentuated by the significantly higher exciton binding energy in the 2D case compared to the 3D ones. We derive temperature‐dependent rate equations to quantitatively explain host‐to‐dopant energy‐transfer dynamics, identifying the role of dark excitonic states in near‐resonant energy‐transfer and back‐transfer processes, establishing a comprehensive understanding of Mn ²⁺ emission in such 2D hybrid lead bromide systems.