High‐Pressure Modulation of NIR Luminescence in Cr 3+ ‐Doped Cs 2 AgInCl 6 Double Perovskites: The Role of Ultrafast Energy Transfer

Abstract Lead‐free halide double perovskites (DPs) have attracted much attention due to their potential applications in the field of near‐infrared (NIR) optoelectronics. However, regulating the NIR luminescence properties of such materials remains a challenge. In this study, it is found that Cs 2 AgInCl 6 :Cr 3+ DPs exhibit a broad NIR emission under ultraviolet excitation, with a peak value of 980 nm. In the range of 9 GPa, the emission intensity increases significantly. As the pressure increases, a transition from broadband NIR emission to narrow‐line emission occurs, accompanied by a decrease in the full width at half maximum (FWHM) from 260 to 40 nm, attributed to increased local structural asymmetry and enhanced crystal field around Cr 3+ ions. Ultrafast transient absorption experiments reveal the changes of energy transfer under pressure and the emergence of new radiation channels, demonstrating the dynamic evolution of emission characteristics under high pressure. The research results deepen the understanding of high pressure luminescence in Cr 3 ⁺‐doped halide DPs, providing strategies for designing highly efficient NIR emitters in metal halide DPs.