“…Therefore, it is quite meaningful to measure temperature with high spatial and temperature resolution. Recently, some efforts have been focused on the study of the temperature-dependent rare earth (RE) ions doped anti-Stokes (or upconversion, UC) emission or transition-metal (TM) ions doped Stokes emission material owing to their significant potential application in noncontact temperature sensors. − Generally, optical parameters, such as the fluorescence intensity, the peak wavelength, the emission bandwidth, the fluorescence intensity ratio (FIR), as well as the fluorescence lifetime, can be adopted to detect temperature. − Unfortunately, the fluorescence intensity, the peak wavelength, and the emission bandwidth are strongly affected by the external factor, such as light source, atmosphere, and pressure. In contrast, FIR-based temperature sensors exhibit a high measurement accuracy and reliability because FIR is independent of spectral losses and fluctuations in the excitation density.…”