Reversible photoluminescence switching in photochromic material Sr6Ca4(PO4)6F2:Eu2+ and the modified performance by trap engineering via Ln3+ (Ln = La, Y, Gd, Lu) co-doping for erasable optical data storage
Reversible photoluminescence switching based on photochromism has drawn considerable interests and concerns benefited from its widespread promising applications for photo-switching, anti-counterfeiting and optical information storage. In this paper, we reported a novel photochromic material Sr6Ca4(PO4)6F2:Eu2+ which exhibits reversible photoluminescence switching ability. The coloration and bleaching, which are attributed to the capture and release of electrons by traps, respectively, can be efficiently converted accompanied with the color change between pink and white upon alternating UV light irradiation and visible light irradiation or thermal treatment. The photochromic property of Sr6Ca4(PO4)6F2:Eu2+ shows high reversibility and excellent fatigue resistance. Trap engineering allows an effective way to modify the traps through changing the Eu2+ doping content and co-dopants Ln3+ (La, Y, Gd, Lu) ions, thereby purposely controlling the performance of photochromism. The photoluminescence switching strongly depends on photochromic effect and exhibits a good reversibility after several cycle measurements. The relative photoluminescence intensity measured from a partially thermal bleaching state indicates the highest instantaneous temperature suffered by the sample, indicating the good application prospect in the instantaneous temperature recording. In addition, various patterns can be repeatedly recorded in the photochromic material Sr6Ca4(PO4)6F2:Eu2+ by alternative UV light and visible light/heat treatment, demonstrating potential application for erasable optical data storage.