Theoretical model and verification of the laser thermal effect on the temperature measurement sensitivity of rare earth

The fluorescence temperature measurement based on rare earth ions has been studied widely. It is quite puzzling that the same thermal coupling energy levels present different relative sensitivities of temperature measurement in reports. Different relative sensitivities indicate that the level spacing of the same thermal coupling energy levels calculated by Boltzmann`s formula is different. To solve this problem, a physical model is proposed to explain the influence of the laser thermal effect on the fluorescence temperature measurement. The results show that the additional temperature of the sample imposed by the laser thermal effect has an impact on the relative sensitivity, which is the higher the additional temperature, the lower the relative sensitivity. Furthermore, the source of heat generation from laser irradiation of rare earth is discussed. For Er ³⁺ ions, the laser converted into heat mainly generated by the multiphonon transitions between ²H _11/2 and ⁴S _3/2 levels. The results show that the theoretical curve fitted well with the experimental data. It is instructive for the design of new temperature sensors.