Lead‐Free Perovskites with Photochromism and Reversed Thermochromism for Repeatable Information Writing and Erasing

Abstract Recently, novel optical information writing strategies have been developed based on fluorescent change of halide perovskites generated by light induced structural transformation. However, to date, the repeatable writing and erasing of fluorescent patterns are still a major challenge. Herein, lead‐free Cs ₃ InCl ₆ :Sb ³⁺ perovskite with photochromism and reversed thermochromism is developed for repeatable information writing and erasing. The original Cs ₃ InCl ₆ :Sb ³⁺ perovskite synthesized by a modified hot‐injection method exhibits green photoluminescence (PL), which is caused by recombination of self‐trapped excitons. After treating with ultrasonication and heating, the green PL gradually turns to blue emission, which is related to surficial Cl vacancies that are generated or exposed due to the desorption of surfactants. Under continuous UV light irradiation, due to the photo repairing effect, the blue emission gradually vanishes, the fluorescent color recovers to green. Based on this photochromic effect, fluorescent patterns are drawn by UV exposure with mask. Moreover, the green PL color can again return to blue by heating at 100 °C. Thus, the photochromism‐induced fluorescent patterns can be simply erased based on the reversed thermochromism effect. Therefore, repeatable optical information writing and thermal erasure are demonstrated based on reversible PL change of Cs ₃ InCl ₆ :Sb ³⁺ .