Regulating A-Site Alloying of Cs _2-x Rb _<i>x</i> InBr ₅ ·H ₂ O Perovskites for NIR LED Applications

Lead-free halide perovskites have drawn considerable interest, owing to their low-toxicity and favorable photophysical characteristics. However, achieving efficient near-infrared (NIR) emission often suffers from a trade-off between the red shift and quantum yield. Herein, we report a synergistic host-dopant strategy in zero-dimensional Cs2-xRbxInBr5·H2O perovskites. Controlled Rb+ alloying induces lattice contraction, which unexpectedly weakens electron–phonon coupling and suppresses nonradiative decay, leading to a high photoluminescence quantum yield (PLQY) of 53.2%. Subsequently Mn2+ doping further passivates defect states, boosting the PLQY to 67.5%. Density functional theory calculations and temperature-dependent spectroscopy elucidate the role of the lattice strain in regulating self-trapped exciton emission. A prototype NIR phosphor-converted light-emitting diode (pc-LED) fabricated from the optimized material demonstrates a promising performance in night-vision imaging and plant growth applications. This work provides a viable design strategy for efficient and stable NIR phosphors via a coupled lattice and defect engineering.