Long Persistent Luminescence in Cu²⁺-Doped SrGa₂Ge₂O₈ for Information Storage and Encryption

Information storage and encryption are the key technologies for modern information transmission. However, most optical information storage technologies based on long persistent luminescent (PersL) only have one fixed response mode, which is easy to imitate, limiting their security in advanced information storage and encryption applications. Besides, the cost of rare earth-doped PersL materials restricts their wide application. Therefore, exploring non-rare earth-doped multimode PersL phosphors is an urgent and important topic. In this work, a novel SrGa₂Ge₂O₈:Cu²⁺ (SGGO:Cu²⁺) phosphor with yellow-green PersL at 535 nm and near-infrared emission excited by ultraviolet light is designed. Furthermore, the two luminescence peaks of SGGO:0.007Cu²⁺ exhibit discriminable thermal quenching characteristics. Prominently, an outstanding photochromic performance from white to gray within 60 s under 254 nm light is found. The phosphor also has good bleaching and recovery ability under the irradiation of 450 nm blue light or heating treatment. Finally, the yellow-green PersL combined with thermochromism and reversible white-to-gray photochromism provides a promising multimode luminescent material, demonstrating the potential for multimode optical information storage and encryption applications.