Strong Self-Trapped Exciton Emission and Highly Efficient Near-Infrared luminescence in Sb³⁺-Yb³⁺ Co-doped Cs₂AgInCl₆ Double Perovskite

Yb³⁺ doped lead-free double perovskites (DPs) with near-infrared (NIR)-emitting have attracted extensive attention due to their wide application prospects. Unfortunately, they still suffer from weak NIR emission due to undesirable resonance energy transfer between the sensitizers and Yb³⁺ ions. Herein, a new effective NIR-emitting DP is developed by co-doping Sb³⁺ and Yb³⁺ into Cs₂AgInCl₆. Experiments and theoretical calculations reveal that induced by co-doping Sb³⁺ ions, the self-trapped excitation (STE) emission intensity of Cs₂AgInCl₆ is greatly enhanced by 240 times, and the STE emission shifts from 600 nm to 660 nm, which contributes to a larger spectral overlap between STE emission and the absorption of Yb³⁺ ions. As a result, the absolute NIR photoluminescence quantum yield reaches an unprecedented 50% in lead-free DPs via high-efficiency STE sensitization (>30%). The excellent optical performance of Cs₂AgInCl₆: Sb, Yb with high ambient, thermal and light stability makes it suitable for application in night-vision devices. Moreover, an ingenious dual-modal optical information encryption based on the combination of visible and NIR fluorescence printing patterns utilizing Cs₂AgInCl₆: Sb and Cs₂AgInCl₆: Sb, Yb respectively is successfully demonstrated. This study provides inspiration for designing highly efficient NIR-emitting Ln³⁺-doped DPs and illustrates their great potential in versatile optoelectronic applications.