Upconversion photoluminescence properties of ZrO2: Ln3+/Yb3+ (Ln = Er, Ho, Tm) films formed by plasma electrolytic oxidation

Abstract

The highly-efficient upconversion photoluminescent ZrO2:Ln3+/Yb3+ (Ln = Er, Ho, Tm) films were prepared by the plasma electrolytic oxidation method from the pure zirconium foil, by adding Ln2O3 and Yb2O3 particles to the supporting electrolyte, in various concentrations. The method of synthesis, morphology, chemical, and phase composition of formed films were described and discussed. All the samples exhibit visible upconversion photoluminescence (PL) after 980 nm irradiation, which matches with the energy of the excited level of Yb3+. The upconversion PL mechanism and dependence of upconversion PL properties on Ln2O3 and Yb2O3 concentrations in supporting electrolyte that is, concentrations of Ln3+ and Yb3+ in formed films, was investigated. The upconversion PL intensity of ZrO2:Ln3+/Yb3+ films rises as Yb3+ concentration increases due to efficient energy transfer from Yb3+ to Ln3+. The emission color of Er3+ and Ho3+ in ZrO2:Er3+/Yb3+ and ZrO2:Ho3+/Yb3+ films, respectively, can be fine-tuned by adjusting the Yb3+ concentration. The ratios 4F9/2→4I15/2 / 4S3/2→4I15/2 of Er3+ and 5F4,5S2→5I8 / 5F5→5I8 of Ho3+ increase significantly with increasing Yb3+ content.