Reversible white-purple photochromism in europium doped Sr3GdLi(PO4)3F powders

Inorganic photochromic materials have attracted growing attention in recent years. Here, a reversible white-purple photochromic powder material Sr3GdLi(PO4)3F:Eu2+ was synthesized by conventional solid-state method. The surface color shows reversible white-purple changes after irradiated alternatively by UV and visible light (or thermal treat). Diffuse reflectance spectra were used to characterize the photochromic properties including coloring and bleaching. The results indicated that the optimal Eu2+ doping concentration was found to be about 0.5 mol%. Several cycles measurements including photo- and thermal-induced bleaching indicates that Sr3GdLi(PO4)3F:Eu2+ posses high fatigue resistance in photochromism performance. Based on thermoluminescence curves, the photochromism property related factors that the critical role of traps and the motion of charge carriers between traps were discussed. Finally, a schematic diagram for illustrating the photochromic mechanism was proposed.