Up-conversion luminescence behaviors in Er³⁺ doped single crystal KNbO₃ nanosheets

Perovskite oxides have attracted much attention owing to their excellent physical properties, such as piezoelectricity, ferroelectricity, and ferromagnetism. Moreover, these properties can be strongly affected and regulated by the doping strategy. In this work, Er³⁺ doped single crystal KNbO₃ nanosheets were successfully synthesized via a solvothermal method. XRD analysis indicated that Er³⁺ firstly substituted into the B site (Nb⁵⁺) and then A site (K⁺) in the ABO₃ perovskite structure with the further increasing content of Er³⁺. The orthorhombic structure of the pure KNbO₃ and Er³⁺ doped KNbO₃ was proved in terms of the Raman spectra. The SEM observation demonstrated that the size of the as-obtained nanosheets was about 70 nm in thickness and 3 μm in diameter. The single crystal structure state of the as-obtained products was confirmed by HRTEM. Furthermore, the growth mechanism of Er³⁺ doped KNbO₃ nanosheets was rationally elaborated and proposed. The as-obtained Er³⁺ doped KNbO₃ nanosheets exhibited excellent up-conversion (UC) photoluminescence (PL) properties with a strong green emission and a weak red emission. The maximum emission intensity of the UC PL spectrum was achieved with 0.4 mol% of Er³⁺ doped. To conclude, the as-synthesized Er³⁺ doped KNbO₃ nanosheets could be a potential candidate for the development of multifunctional devices, by introducing PL properties to piezoelectric KNbO₃ materials.