Unveiling the Mechanisms of Photoluminescence Quantum Yield Surge in Cs2AgInCl6 Nanocrystals Triggered by ∼0.8% Bi3+ Doping

Bi doping in Cs2AgInCl6 nanocrystals (NCs) has attracted significant attention; however, the fundamental origins of its enhanced luminescence remain elusive. This study explores the key mechanisms behind the photoluminescence quantum yield (PLQY) enhancement induced by Bi doping in Cs2AgIn1–xBixCl6 NCs. Remarkably, just ∼0.8% Bi doping elevates PLQY to ∼40%. Through a synergistic approach combining Raman spectroscopy, UV–vis absorption, photoluminescence, and density functional theory (DFT), we reveal that this enhancement stems from a unique interplay of direct bandgap, increased lattice polarizability, strong electron–phonon coupling, and minimized nonradiative losses. Femtosecond transient absorption and time-resolved photoluminescence measurements exposed a marked suppression of nonradiative recombination and prolonged carrier lifetimes in Bi-doped samples, affirming the structural and electronic advantages introduced by doping. Our findings offer a complete comprehensive picture of both the static and dynamic photophysics of Cs2AgIn1–xBixCl6 NCs.