Manipulation of the ratio of Li+/Zn2+ on the structure and persistent luminescence property of Li2Zn0.9992Ge3O8:0.08%Cr3+

Long persistent luminescence (LPL) materials have been widely applied and investigated in the fields of night-safe, bio-fluorescent labeling, and optical anti-counterfeiting because of their unique properties of delayed luminescence. In this work, the focus of this research is to significantly improve the LPL properties of Li2Zn0.9992Ge3O8:0.08%Cr3+ by adjusting the ratio of Li+/Zn2+. On the one hand, when Li+:Zn2+ < 2:1 (Li1.97Zn1.0292Ge3O8:0.08%Cr3+), a deep-red LPL is produced in the 650-900 nm band for more than 50 h, which is 2.5 times longer than that without regulation. From another perspective, when Li+:Zn2+ > 2:1 (Li2.01Zn0.9892Ge3O8:0.08%Cr3+), the intensity of LPL is enhanced about four times compared to unregulated. The relationship between traps and LPL was comprehensively investigated by analyzing thermoluminescence spectra. Biological tissue penetration experiments were performed and a set of anti-counterfeit labels was designed. This research will provide guidance for the design of a novel persistent phosphor for the desired trap depth.