Type I band alignment and defect-color center synergy strategy to strengthen the photoluminescence and photochromism for high-entropy aluminate-based phosphors

The development of multimodal anti-counterfeiting materials integrating photoluminescence and photochromic functions holds great significance for dynamic anti-counterfeiting and information storage. Nevertheless, traditional single-component systems typically encounter issues such as limited luminescence efficiency and a lack of diversity in color regulation methods. In this research, multi - dimensional regulation of optical properties was accomplished by fabricating a type I heterojunction of the Ba 0.5 Sr 0.5 TiO 3 (BST5)/high entropy spinel (Cd 0.2 Mg 0.2 Cu 0.2 Co 0.2 Ni 0.2 )Al 2 O 4 ((CdM)A). Phase structure and spectroscopic characterizations demonstrated that the interfacial strain remarkably facilitated the enrichment of oxygen vacancies and actuated the reversible transformation between Ti 4⁺ /Ti 3⁺ and Co 3⁺ /Co 2⁺ . This defect - color center synergistic effect not only remarkably enhances the fluorescence emission intensity but also imparts a reversible photochromic response to the sample. Further analysis indicates that the local lattice distortions and defects induced by the high entropy effect effectively enhance the efficiency of carrier migration and energy transfer. As a result, the composite system demonstrates stable cyclic luminescence - color change coupling properties under multi - wavelength excitations at 254, 302, and 365 nm. This research uncovers a unified mechanism characterized by type I band alignment and the synergy of oxygen vacancy (O V )/Ti³⁺/Co²⁺, thereby furnishing a solid theoretical foundation and compelling experimental evidence for the design of novel multi-modal dynamic anti-counterfeiting materials.