Boosting the photochromic property of KSr₂Nb₅O₁₅-based ceramics through an indirect vacancy-regulation strategy

KSr₂Nb₅O₁₅ (KSN)-based photochromic ceramics are highly anticipated for potential applications in optical data storage and anti-counterfeiting owing to their reversible change in optical performance after light irradiation. However, the limited photochromic property of KSN has hindered its further development, and the intrinsic contradiction between the carrier-trap content and depth has restricted improvements in photochromic performance through direct regulation of vacancy-related defects. To overcome these challenges, an indirect vacancy-regulation strategy was proposed. This strategy involves substituting a portion of Sr²⁺ in KSN lattice with volatile Li⁺, promoting the generation of additional cation vacancies through Li⁺ evaporation, and increasing oxygen vacancy formation via the charge-balance process of acceptor doping. Results showed that the photochromic contrast values of KSN-based ceramics nearly tripled compared with their original value (from 8.18 % to 23.39 %) through indirect vacancy-regulation. This strategy effectively resolved the intrinsic contradiction for trap modification by increasing the concentration of effective color centers and controlling the distribution of vacancy defects. Atomic-scale analysis revealed that acceptor doping and oxygen vacancy formation tend to occur at or around the A1 sites of the KSN lattice. The indirect vacancy-regulation strategy maintained a relatively uniform distribution of defects and prevented any evident damage to the original electronic structure of the lattice. This work is expected to provide a valuable reference for modifying inorganic photochromic materials and deepen the understanding of the photochromic mechanism.