Unlocking The Inherent Luminescence of Eu²⁺/Eu³⁺ by Light-Induced Oxidation for Invisible Optical Storage

Color-tunable luminescent materials are increasingly recognized for their potential applications in high-security anticounterfeiting and optical storage technologies. However, luminescent materials with high-contrast photoswitching behavior that change their luminescence properties in response to external stimuli are extremely scarce. In this study, a time-dependent color-tunable luminescent material, Na2BaSiO4:Eu2+ (NBSO:Eu), is introduced. This material leverages the inherent luminescence of Eu2+/Eu3+ through a light stimulus. Under 365 nm irradiation, the blue luminescence of Eu2+ gradually degraded over time, reaching a luminescence contrast of up to 88%. This degradation is accompanied by a color change of the emitted light from blue to red (Eu3+). These color changes can be reversibly tuned by alternating light or thermal stimuli. Experimental investigations revealed that the photogenerated Eu3+ ions and defects, acting as killer centers, induced multicolor luminescent switching behavior. Owing to their unique optical properties, NBSO:Eu offers exciting opportunities for designing advanced dynamic anticounterfeiting and invisible optical storage.