Spectral characteristics and optical temperature sensing properties of Er³⁺/Yb³⁺-co-doped phosphate glasses with GeO₂ modification

E r 3 + / Y b 3 + -co-doped phosphate glasses with G e O 2 modification (PLAZGs) were successfully prepared by the melt-quenching method. The phenomenological intensity parameters Ω t ( t = 2 , 4, 6) of the PLAZGs have been calculated by the Judd–Ofelt theory. Based on the phenomenological intensity parameters, the spectroscopic parameters of E r 3 + and fluorescence intensity ratio (FIR) of green upconversion emissions were estimated. It was observed that, under 980 nm excitation, all samples exhibit green and red upconversion emissions of E r 3 + . The 10 mol% G e O 2 modified phosphate glass has the strongest upconversion emission. Additionally, the fluorescence decays of the 2 F 5 / 2 → 2 F 7 / 2 transition of Y b 3 + ions were measured to evaluate the energy transfer efficiency from Y b 3 + to E r 3 + ions. Finally, the optical temperature sensing properties based on upconversion emissions were investigated at temperatures from 150 K to 600 K. The maximum absolute temperature sensitivity S value of 6.0 × 1 0 − 3 K − 1 at 400 K is obtained, which indicates that the glass is promising for temperature sensing application based on the FIR technology.