Optical temperature-sensing properties in La1.55SiO4.33:Yb3+,Ho3+ phosphors affected by Ho3+-doping concentration

In this paper, the Yb3+-Ho3+ co-doped La1.55SiO4.33 (LSO) phosphors were synthesized by the conventional solid-state reaction method. The phase purity and morphology of the samples were studied by XRD and SEM, respectively. Under 980 nm excitation, the upconversion (UC) luminescence of the LSO:Yb3+,Ho3+ phosphors was checked for different Ho3+ doping content and pump power. The corresponding UC mechanism was interpreted from the changing decay lifetimes and the energy transfer processes between Yb3+ and Ho3+ ions. Meanwhile, the temperature-dependent emission spectra were analyzed to learn the optical temperature-sensing behaviors with the fluorescence intensity ratio (FIR) method. The results revealed that the FIR (I658/I544) value increased when the temperature rose, which followed a linear function. The sensor sensitivity was evaluated, and the LSO:10%Yb3+,2%Ho3+ phosphor showed the highest absolute sensitivity. Besides, the main population way on 5F5 level of Ho3+ for red emission was clarified by the comparison of the UC spectra excited by continuous-wave and pulse light. Based on the above results, the LSO:Yb3+,Ho3+ phosphor can be considered as a new UC luminescent material for optical temperature sensors.