Abstract Yb 3+ 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 Yb 3+ ions. Herein, a new effective NIR‐emitting DP is developed by co‐doping Sb 3+ and Yb 3+ into Cs 2 AgInCl 6 . Experiments and theoretical calculations reveal that induced by co‐doping Sb 3+ ions, the self‐trapped excitation (STE) emission intensity of Cs 2 AgInCl 6 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 Yb 3+ 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 Cs 2 AgInCl 6 : 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 Cs 2 AgInCl 6 : Sb and Cs 2 AgInCl 6 : Sb, Yb respectively is successfully demonstrated. This study provides inspiration for designing highly efficient NIR‐emitting Ln 3+ ‐doped DPs and illustrates their great potential in versatile optoelectronic applications.