Fiber Optical Temperature Sensor Based on 980nm Excitation of CaWO₄: Yb³⁺, Er³⁺ with Up-conversion Fluorescence Intensity Ratio

Abstract The Yb 3+ , Er 3+ co-doped calcium tungstate materials were prepared. The temperature-sensitive fiber optic probes made from CaWO 4 :Yb 3+ , Er 3+ were prepared by the high-temperature solid-phase sintering method. The XRD lattice structure of CaWO 4 : Yb 3+ , Er 3+ was tested. The fluorescence spectra of the probe under 980nm excitation were tested, and the variable temperature profile of the probe was analyzed to derive its two-photon absorption process. The temperature characteristics of the up-conversion fluorescence intensity ratio (FIR) of the probe in the temperature range of 303-673K were investigated, and the results showed that this optical fiber probe can be used as a fiber optic temperature sensor with a linearity of 5.8% and a temperature measurement return difference of only 1.5%; it was found that the temperature characteristic curve of FIR of this fiber optic probe was reproducible. These properties show that CaWO 4 : Yb 3+ , Er 3+ is feasible to be made into a fiber optic sensor.