Optical temperature-sensing properties in La1.55SiO4.33:Yb3+,Ho(3+)phosphors affected by Ho3+-doping concentration

In this paper, the Yb3+-Ho3+ co-doped La1.55SiO4.33 (LSO) phosphors were synthesized by the conventional solidstate 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 Ho(3+ )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 (I-658/I-544) 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 F-5(5) level of Ho3+ for red emission was clarified by the comparison of the UC spectra excited by continuouswave 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.