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

Abstract

Reversible photoluminescence switching based on photochromism has drawn considerable interest due to its widespread promising applications in photo-switching, anti-counterfeiting and optical information storage. In this paper, we reported a novel photochromic material Sr₆Ca₄(PO₄)₆F₂:Eu²⁺ which exhibits the reversible photoluminescence switching ability. Coloration and bleaching, which are attributed to the capture and release of electrons by traps, respectively, can be efficiently converted accompanied by the color change between pink and white upon alternating UV light irradiation and visible light irradiation or thermal treatment. Sr₆Ca₄(PO₄)₆F₂:Eu²⁺ shows photochromic properties such as high reversibility and excellent fatigue resistance. Trap engineering allows an effective way to modify the traps through changing the Eu²⁺ doping content and co-dopant Ln³⁺ (La, Y, Gd, Lu) ions, thereby purposely controlling the performance of photochromism. Photoluminescence switching strongly depends on the photochromic effect and exhibits a good reversibility after several cycles of 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 prospects in 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 in erasable optical data storage.