Optical thermometry through green upconversion emissions in Er ³⁺/Yb ³⁺-codoped CaWO ₄ phosphor

Under 980nm excitation, the temperature-dependent green upconversion emissions from Er ³⁺/Yb ³⁺-codoped CaWO ₄ phosphor were studied at temperatures from 294 to 923 K. By using the fluorescence intensity ratio technique, the maximum sensitivity for temperature measurement achieved here is approximately 0.0092 K ^-1, which is much higher than previously reported temperature sensors based on the fluorescence of Er ³⁺ions in other host materials. With the efficient upconversion fluorescence, the Er ³⁺/Yb ³⁺-codoped CaWO ₄ is a very promising candidate for optical high-temperature sensors with high sensitivity and good accuracy.