Mechanisms of photochromism and optical properties in Sm3+-doped K0.5Na0.5NbO3 ceramics

Due to their potential applications in optical information storage, optical switches, and related fields, transparent photochromic materials have attracted significant attention. However, most current studies on rare-earth-doped K 0.5 Na 0.5 NbO 3 (KNN)ceramics focus on macroscopic photochromic phenomena, while in-depth investigations into the underlying microscopic mechanisms remain limited. This study fabricated Sm 3+ -doped K 0.5 Na 0.5 NbO 3 transparent ceramics using a high-temperature solid-state method at various sintering temperatures and systematically investigated the influence of sintering temperature on their microstructure, optical transmittance, and photochromic behavior to gain deeper insight into the essence of photochromism. Compared to previous studies that primarily addressed luminescence or visual color changes, this study combines X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) lifetime analysis, and thermal cycling to elucidate the formation and role of vacancy-trapped electron centers. The results showed that the ceramics exhibited maximum transmittance values of 44 % and 60 % at 597 and 900 nm, respectively, at a sintering temperature of 1185 °C. A transmittance modulation ratio of 23 % at 597 nm was achieved at 1170 °C. Alternating light and thermal stimuli enabled reversible modulation of luminescence intensity and transmittance, demonstrating excellent stability and repeatability. X-ray photoelectron spectroscopy revealed that photo-induced color centers formed by vacancy-trapped electrons reduced the transmittance and emission intensity, elucidating the intrinsic photochromic mechanism. Therefore, these ceramics showed strong potential for applications in optical data storage and nondestructive optical readout.