The making and breaking of perovskite photochromism through doping

Photochromic single crystals of high transparency are considered as basic building blocks for many advanced applications, such as three-dimensional optical storage and volumetric displays. In this work, a transparent crystal of Cs₂AgInCl₆ perovskite was grown in a hydrothermal reactor. A high transmittance-contrast degree up to 30% was achieved by photochromism activation via a Mn²⁺-doping strategy. Intriguingly, both coloration and decoloration could be triggered by light at appropriate wavelengths, 365 nm and 520 nm for example. Unlike heat-induced decoloration, the optical route represents a much faster tool to erase information. As a caveat from photochromism, the photoluminescence quantum yield (PL QY) was significantly decreased down to 1.7%. In an attempt to boost the quantum yield, sodium ions were introduced as a co-dopant. Surprisingly, the co-doping strategy not only boosted the PL QY to 33%, but also deactivated the photochromism. Our work expanded the library of photochromic materials by introducing a new perovskite single crystal, representing a paradigm for the making and breaking of photochromism.