Enhanced Photochromism and Thermochromism in Zirconium Halide Perovskite through Bismuth Doping and Thermal Recrystallization

Abstract Photochromic/thermochromic materials face challenges in practical applications due to limited stability and single‐mode responses. Herein, a strategy is presented to achieve both highly stable photochromism and thermochromism in a single‐phase Cs₂ZrCl₆ halide perovskite through trap and energy level manipulation via Bi 3 ⁺ doping and thermal recrystallization. Strikingly, the synthesis of this allochroic perovskite is expeditious, requiring only ≈10 s via a co‐precipitation method. Bi 3 ⁺ doping creates unique defects with a broad trap depth distribution, resulting in highly stable photochromic properties. Upon UV irradiation (254 or 365 nm), the color of Cs₂ZrCl₆:0.02Bi 3 ⁺ changes from white to pink, which can be physically visible to the naked eye with a luminance of ≈50 cd m − 2 and maintained >20 days under ambient light. Additionally, a thermochromic response is observed, with the photoluminescence shifting from blue to cyan after being kept at 523 K, associated with a ≈20 nm redshift in the emission band. These dual allochroic properties enable the potential use for multimodal information storage and advanced anti‐counterfeiting applications. This work not only introduces a novel Cs₂ZrCl₆ perovskite with dual allochroic capabilities but also provides new insights into the design of allochroic materials through strategic trap and energy level engineering.