Solution‐Grown Chloride Perovskite Crystal of Red Afterglow

We report the growth of a halide-based double perovskite, Cs2 Nax Ag1-x InCl6 :y%Mn, via a facile hydrothermal reaction at 180 °C. Through a co-doping strategy of both Na+ and Mn2+ , the as-prepared crystals exhibited a red afterglow featuring a high color purity (ca. 100 %) and a long duration time (>5400 s), three orders of magnitude longer than those solution-processed organic afterglow crystals. The energy transfer (ET) process between self-trapped excitons (STE) and activators was investigated through time-resolved spectroscopy, which suggested an ET efficiency up to 41 %. Importantly, the nominal concentration of dopants, especially in the case of Na+ , was found a useful tool to control both energy level and number distribution of traps. Cryogenic afterglow measurements suggested that the afterglow phenomenon was likely governed by thermal-activated exciton diffusion and electron tunneling process.