High-efficiency upconversion luminescence and enhanced sensitivity temperature sensing behavior in Ho3+/Yb3+ doped yttrium Oxysulfide phosphors

A series of Y 2 O 2 S: 0.25 % Ho 3+ /x%Yb 3+ (where x = 4, 6, 8, and 10) phosphors were synthesized by using a chemical co-precipitation method, and their temperature sensing properties were systematically investigated. The upconversion luminescence (UCL) spectra of the samples were recorded under 980 nm laser excitation. The Y 2 O 2 S: Ho 3+ /Yb 3+ system exhibits three distinct UC emission bands in the green, red, and near-infrared regions, corresponding to the transitions of 5 F 4 / 5 S 2  →  5 I 8 , 5 F 5  →  5 I 8 , and 5 F 4 / 5 S 2  →  5 I 7 of Ho 3+ , respectively. According to the emission spectra, the sample with a Yb 3+ doping concentration of 6 % exhibited the strongest luminescence intensity, with a quantum yield reaching 4.01 %. To further explore its temperature sensing properties, the fluorescence intensity ratios (FIR) of both thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) of Ho 3+ were systematically analyzed. Notably, temperature sensing materials based on NTCLs exhibit significantly enhanced sensitivity while maintaining a broad temperature measurement range. Specifically, the absolute sensitivity (S A ) increased from 0.011 % to 0.498 %, representing an approximately 45-fold improvement. These findings indicate that Y 2 O 2 S: Ho 3+ /Yb 3+ UCL materials possess excellent potential for applications in optical temperature sensing.