Ultranarrow NIR bandwidth and temperature sensing of YOF:Yb³⁺/Tm³⁺ phosphor in low temperature range

Owing to few thermal populations or spectral absence at extreme low temperature, fluorescence intensity ratio (FIR) technique based on thermal coupling levels is sometimes unpractical for low temperature sensing. Herein, using bandwidth as a sensing parameter, the low temperature sensing performances of YOF:Yb³⁺/Tm³⁺ phosphor are reported. The YOF:10%Yb³⁺/0.2%Tm³⁺ phosphor is prepared by hydrothermal and calcined methods. Under 980 nm excitation, the temperature dependent upconversion spectra are recorded in the range of 12–300 K, and the temperature sensing behaviors are investigated in detail. The phosphor exhibits a single-band near-infrared (NIR) luminescence composed of multiple narrow peaks. Thereinto, the ultranarrow bandwidths of 12,485 cm⁻¹ (800.9 nm) and 12,580 cm⁻¹ (794.9 nm) emission bands are only 14 cm⁻¹ (0.9 nm) and 12 cm⁻¹ (0.75 nm) at 12 K, respectively. Based on temperature dependent bandwidth, the maximum relative sensitivities are found to be 0.60% K⁻¹ (12–190 K) and 0.84% K⁻¹ (190–300 K), which enable the YOF:10%Yb³⁺/0.2%Tm³⁺ phosphor to be a promising thermometer for low temperature sensing.