Near‐Infrared Afterglow and Related Photochromism from Solution‐Grown Perovskite Crystal

Abstract Near‐infrared (NIR) afterglow is keenly sought in emerging areas including deep‐tissue imaging and night‐vision surveillance, while only few successes in powder phosphors are achieved through solid‐state calcination. In this work, a perovskite single crystal, namely Cs 2 Na 0.2 Ag 0.8 InCl 6 :Yb 3+ , is grown in solution via a simple hydrothermal reaction. Through a co‐doping strategy involving both Na + and Yb 3+ , dual‐band emission in the visible and NIR region is activated by self‐trapped excitons (STE) and lanthanide ions, respectively. Importantly, the total photoluminescence quantum yield (PL QY) of both bands is boosted to ≈ 82%. Intriguingly, a long‐lasting afterglow at the NIR band ( ≈ 7200 s) and a simultaneous photochromism is observed after ceasing the excitation. Importantly, the transparency of crystals exhibit a pronounced contrast in the decoloration process, enabling a quantitative analysis of photochromism at varied temperatures. On the other hand, the transparent crystals enable the design of a light‐storage battery free of reabsorption, featuring a linear power output with crystal loading. This work proposes a new paradigm to quantitatively correlate the afterglow traps to photochromism, opening many possibilities to practical applications of NIR‐afterglow transparent crystals.