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. A new design strategy of Sb3+ ions co‐doping in Cs2AgInCl6:Yb3+ is proposed to expand absorption region to longer wavelengths and effectively enhance the near‐infrared emission of Yb3+ ions. The excellent sensitization efficiency from self‐trapped exciton to Yb3+ ions (>30%) gives Sb3+, Yb3+ co‐doped Cs2AgInCl6 unprecedented near‐infrared emission with a photoluminescence quantum yield of up to 50%.