Photochromic properties and mechanism of Mn2+-doped Cs2AgInCl6 double perovskite halides: Impact of synthesis route

Lead-free halide double perovskites have attracted significant attention due to their outstanding optical properties. The integration of photoluminescence and photochromic behavior further broadens their potential applications. However, the underlying photochromic mechanism of Cs 2 AgInCl 6 remains poorly understood, and the influence of the synthesis route on its photochromic performance has not been thoroughly investigated. Herein, Mn 2+ -doped Cs 2 AgInCl 6 phosphors were synthesized via two distinct wet-chemical approaches. It was found that different synthesis routes lead to variations in the initial sample color, which are closely related to the proportion of metallic silver (Ag 0 ) formed during synthesis. Upon irradiation with 365 nm ultraviolet light, the sample color transitions from white (or lavender) to grayish-purple. The coloration mechanism of the former is attributed to the synergistic effects of the Ag + to Ag 0 valence transformation and the formation of color centers associated with chloride vacancies, while the latter is only due to the color centers. A maximum photo-induced coloration contrast of approximately 65 % was achieved, nearly twice that reported for previously studied single-crystal counterparts. Furthermore, the photochromic process enables modulation of the Mn 2+ emission intensity arising from the 4 T 1 → 6 A 1 transition, highlighting the potential of Cs 2 AgInCl 6 : Mn 2+ phosphors in applications such as optical security and solvent recognition.