Luminescence and Photochromic Properties in Eu³⁺-Doped K_0.5Na_0.5NbO₃

K_0.5Na_0.5NbO₃ (KNN) has been widely used as a representative of lead-free ferroelectric perovskite materials. We investigated the luminescence and photochromic properties in Eu³⁺-doped KNN. X-ray diffraction and Rietveld refinement analyses revealed the lattice structures for KNN was to exhibit a mixed phase of orthorhombic, and tetragonal. The intensity of the photoluminescence (PL) was maximized at the Eu³⁺ doping concentration of 5%, which is in good accord with the structural properties of KNN. We also noted variations in PL intensity attributed to the photochromic properties of KNN. The diffuse reflectance in the visible light range has decreased by 17.6% after ultraviolet irradiation, and the PL intensity decreased by 68%. These changes could be restored up to 99% upon heating.