Green and red upconversion luminescence of Er3+-doped K0.5Na0.5NbO3 ceramics

Er3+ doped K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramics were synthesized by the solid-state reaction method. The upconversion emission properties of Er3+ doped KNN ceramics were investigated as a function of Er3+ concentration and incident pumping power intensity. Bright green (~555 nm) and red (670 nm) upconversion emission bands were obtained under 980 nm excitation at room temperature, which are attributed to (2H11/2, 4S3/2)→4I15/2 and 4F9/2→4I15/2 transitions, respectively. The upconversion emission intensity can be adjusted by changing Er3+ concentration, and the mechanism of upconversion processes involve not only a two-photon absorption but also a three-photon absorption. In addition to the admirable intrinsic piezoelectric properties of KNN, this kind of material may have potential application as a multifunctional device by integrating its upconversion and piezoelectric property.