Self Trapped Exciton Emission under Ambient Conditions in Two-Dimensional Halide Double Perovskites Triggered by Heterovalent Metal Substitution

Layered double perovskites (LDPs) possess soft lattice and strong exciton-phonon interactions, which represent an emerging class of materials as promising self trapped exciton (STE) emitters. However, few LDPs have been discovered with observable photoluminescence (PL) under room conditions hindered by the intrinsic parity-forbidden band transition. Herein, manganese (Mn) is incorporated into (PA)₄AgInBr₈ (PA=CH₃(CH₂)₂NH₃₊) to form (PA)₄Ag_1-0.5xMn_xIn_1-0.5xBr₈ (0≤x≤1) heterovalent-metal alloyed layered double perovskites. Halogen substitution is applied to characterize tunable optoelectronic properties of LDPs. Highly oriented thin films are fabricated and investigated via X-ray diffraction 2θ/ω and ψ scan. With this alloy-induced extrinsic exciton self-trapping strategy, broadband emission is obtained under room conditions via tuning STE states from dark to bright. Temperature-dependent PL gives insights to the emissive behavior and charge-carrier dynamics. The associated Huang-Rhys factors and exciton binding energies show the complexity of excitonic localization in this quantum-well-like structure. This study provides inspiration for designing novel lead-free PL-active perovskites and highlights the significance of understanding the intricate details of exciton-lattice coupling dynamics in LDPs.