Photochromism-induced multi-mode optical modulations and fluorescent temperature sensing in Sr/Er-codoped (K0.5Na0.5)NbO3 ceramics†

High-quality (K_0.5Na_0.5)NbO₃ (KNN)-based transparent ceramics are ideal candidates for 3D optical information storage and information anti-counterfeiting encryption. However, conventional single-mode storage and convenient replicability hinder their practical application. Here, by introducing Er³⁺ and Sr²⁺ into a KNN matrix, xSr-1Er-KNN translucent ceramics were prepared, and reversible modulations of ceramic colors, transmittances, down-shifting photoluminescence (DSPL) and up-conversion photoluminescence (UCPL) were achieved. At room temperature, the photochromic (PC) behavior induced high modulation contrasts of both 88% for dual-mode DSPL and UCPL under the excitations of 485 and 980 nm, respectively, exhibiting excellent multi-optical information storage. Moreover, the xSr-1Er-KNN ceramics showed conspicuous low-temperature optical temperature sensing performance through fluorescence intensity ratio technology (a maximum relative sensitivity of 0.023 K⁻¹ was obtained at 213 K). The Er³⁺ and Sr²⁺ codoping in KNN not only improved the transmittance but also enriched intermediate trap levels to significantly increase the number of color centers, and improve the PC contrast and modulation degrees of both the DSPL and UCPL intensities. The potential applications of the xSr-1Er-KNN ceramics at distinct temperatures based on their diverse optical behaviors can guide the development of other optical multifunctional materials and devices.