In the study by Qiwei Zhang, Haiqin Sun, and co-workers (article number 2300925), a time-dependent color-tunable luminescent material (Na 2 BaSiO 4: Eu) is unlocked based on the inherent luminescence of Eu 2+/Eu 3+ through a light stimulus. The blue luminescence of Eu 2+ gradually degrades by 365 nm light irradiation, accompanied by a reversibly emitted color change between blue and red by alternating light or thermal stimuli. Owing to these unique optical properties, the advanced dynamic anti-counterfeiting and invisible optical storage applications can be successfully achieved.