Light-induced phase transition and photochromism in all-inorganic two-dimensional Cs2PbI2Cl2 perovskite

Organic-inorganic hybrid two-dimensional (2D) ruddlesden-popper (RP) perovskites with fantastic optoelectronic properties and good stability have attracted tremendous attention for the potential applications in photovoltaics and electroluminescence. Recently, a new all-inorganic Cs2PbI2Cl2 2D perovskite has been proposed with excellent excitonic absorption and improved ambient and thermal stability. Herein, an interesting light-induced phase transition and photochromism in the Cs2PbI2Cl2 were reported. Under low fluence light pumping, the room temperature photoluminescence (PL) of Cs2PbI2Cl2 is dominated by a weak violet excitonic emission peaked at 412 nm. Surprisingly, the emission color gradually changes from violet to bright red while increasing the laser pumping fluence. This photochromic effect is determined to be caused by forming CsPbI3 phase within the Cs2PbI2Cl2 crystals, which is efficiently driven by thermal energy. Due to protection by the Cs2PbI2Cl2 matrix, the embedded CsPbI3 nanocrystals show improved stability than standard pure CsPbI3. Therefore, the Cs2PbI2Cl2 perovskite with photochromic feature may find applications in optical encryption, as preliminarily shown in this work.