Upconversion luminescence, optical thermometric properties and energy transfer in Yb3+/Tm3+ co-doped phosphate glass

Yb3+/Tm3+ co-doped transparent phosphate glasses were successfully synthesized by conventional melt-quenching method. The upconversion (UC) emission spectra, fluorescence lifetime and transmission spectra were characterized by using UV-visible spectrophotometer and Fluorescence Spectrometer. The results show that the Yb3+/Tm3+ co-doped phosphate glasses are highly transparent with a transmittance of about 90% in the visible light range, and the energy transfer between Yb3+ and Tm3+ occurs. Furthermore, the temperature dependent luminescence of the glasses was systematically investigated to explore the possible application as optical temperature sensors. Using the fluorescence intensity ratio (FIR) technique, the FIR of the UC emissions from 693 nm (Tm3+: 1G4→3H5) and 658 nm (Tm3+: 3F2→3H6) was studied as a function of temperature in the range of 303-653 K, under 980 nm laser excitation. Impressively, the high relative temperature sensitivity of 3.94% K−1 was obtained at 303 K in the Yb3+/Tm3+ co-doped phosphate glass, which is a very promising candidate for optical temperature sensors.