Temperature-dependent upconversion luminescence and spectra characteristic of Er³⁺/Yb³⁺ co-doped fluorotellurite glasses

Er³⁺/Yb³⁺ co-doped fluorotellurite glasses were prepared. Intense green and red upconversion (UC) emissions corresponding to the transitions of ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 were observed under 980 nm laser excitation, benefiting from the advantages of low phonon energy and good stability of fluorotellurite glasses. Temperature-dependent UC luminescence was carried on glasses with different doping concentration of Er³⁺ in the range of 298–568 K. Fluorescence intensity ratios (FIR) and absolute sensitivities (S_a) were calculated, and the maximal sensitivity value of 54.09 × 10⁻⁴ K⁻¹ was obtained at 531 K in the glass with the lowest Er³⁺ concentration at 0.1 mol%. This study indicates that Er³⁺/Yb³⁺ co-doped fluorotellurite glasses can be promising materials applied to non-touching temperature sensors.