Photoelectric Interaction and Photochromic Mechanism\nof K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Ceramics

Rare-earth\nmaterials are widely used in the optical field due to\ntheir rich energy-level structures, and if endowed with photoelectric\nresponse characteristics, they are expected to be applied to photoelectric\nmultifunctional devices. In this paper, Ho<sup>3+</sup>- and Yb<sup>3+</sup>-codoped K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> (KNN)\nferroelectric ceramics are synthesized, and the up-conversion and\ndown-conversion luminescence intensity as well as the decay degree\nafter photochromism can be controlled by the content of Yb<sup>3+</sup>. Strong green luminescence visible to the naked eye is realized,\nand the maximum luminescence decay is more than 50%. 2 s of color\nchange fully indicates that the ceramic has the characteristics of\nfast response photochromic, under the most efficient wavelength of\n405 nm by changing the irradiation wavelength. By incorporating data\nfrom thermal and electrical stimulation experiments, a comprehensive\nphotochromic mechanism diagram is constructed, where the photochromic\nproperties are predominantly governed by defects. It is believed that\nthis work will provide a theoretical basis for the design of high-performance\nphotochromic ceramics.