Photoluminescence and impedance properties of rare-earth doped (K_0.5Na_0.5)NbO₃ lead-free ceramics

Rare earth (RE) elements (Pr, Sm) doped K_0.5Na_0.5NbO₃ (KNN) lead-free ceramics were fabricated using conventional solid-state reaction method and their properties were investigated. The X-ray methods indicate that Pr and Sm ions diffuse into the KNN lattice to form new homogenous solid solutions. After the doping of RE elements, the grain size decreases obviously and the phase structure translates from orthorhombic to pseudo cubic phase. The RE ions enter into the A-site of the KNN lattice to create new A-site vacancies, exhibiting “soft” characteristics. Existence of two semicircular arcs represents both grain and grain boundary property of the materials. The results of E_a indicate that oxygen vacancies dominate the conductivity properties of the ceramics from 425 to 525 °C The photoluminescence spectra of KNN + Pr exhibits orange emissions. Both the KNN + Sm and KNN + Pr/Sm ceramics exhibit yellowish green emission upon 406 nm light excitation. RE elements Pr and Sm-doped KNN ceramics may take an important role in many fields as multifunctional materials.