Light–Heat and Light–Light Dual-Controlled Upconversion Luminescence and Photochromic Processes in Er-Activated Bi7Ti4NbO21 for Optical Information Storage

Upconversion (UC) luminescence materials with dynamically adjustable activity under external stimuli are of great interest owing to their potential applications in optical storage and high-sensitivity optical switches. Recently, photochromic (PC) effect was considered as an alternate way to regulate the UC luminescence of inorganic materials; however, external-field-induced bleaching was routinely completed by single stimulation, which limited its practical application. In this work, one kind of smart phosphor, Er-activated Bi7Ti4NbO21 intergrowth bismuth layer-structured ceramics that exhibited both intense UC green emission and prominent PC reaction, was synthesized. The UC luminescence, PC effect, and their coupling properties were researched. Interestingly, light–heat and light–light dual-controlled UC luminescence and PC processes were realized. Accompanying the PC effect, the UC luminescence can be reversibly modified by alternating 405 and 532 nm light stimulation (or thermal stimulation). Under 405 nm irradiation, the UC luminescence quenching ratio can reach up to 80.8%. Meanwhile, the UC luminescence raise ratio can respectively reach up to 426.9 and 118.1% under 250 °C thermal treatment and 532 nm light bleaching. The UC luminescence modulation was exposed to be tightly related to the irradiation coloration and thermal/light decoloration processes. Good fatigue resistance of the UC luminescence switching was also achieved. The mechanisms related to the UC luminescence modulation and PC process were discussed. These results indicated that Er-activated Bi7Ti4NbO21 samples can be adopted as a kind of optical data memory materials.