Microwave hydrothermal synthesis and temperature sensing behavior of Lu2Ti2O7:Yb3+/Er3+ nanophosphors

Lu2Ti2O7:Yb3+/Er3+ (LTO:Yb3+/Er3+) nanophosphors codoped with Yb3+ (8-20 at%) and Er3+ ions (0.5-4 at%) were synthesized by a microwave hydrothermal process. Under the 980 nm excitation, the sample gives a set of upconversion light: very strong red emissions near 661 nm (4F9/2 → 4I15/2), weak green around 523 nm and 545 nm (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2, respectively). The optimum doping concentrations of Er3+ and Yb3+ for the highest emission intensity were determined by photoluminescence (PL) analyses. Concentration dependent studies revealed that the optimal composition was realized for the 12 at% Yb3+ and 2.0 at% Er3+-doping concentration with a strong emission. A possible UC mechanism for LTO:Yb3+/Er3+ is discussed via the change of the pump power. The temperature dependence of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaked at 523 and 545 nm was studied in the range of 298-573 K under excitation by a 980 nm diode laser and the maximum sensitivity was approximately 0.00313 K−1 at 536 K. This indicates that LTO:Yb3+/Er3+ nanophosphors are potential candidates for optical temperature sensors with high sensitivity.