Temperature sensor based on upconversion luminescence of Er3+-doped fluoroaluminate glasses

New Er3+-doped fluoroaluminate glasses were examined as a host matrix for optical temperature sensors. The upconversion spectra as a function of temperature have been measured in the temperature range from 20 °C (293 K) to 235 °C (508 K). The nature of the upconversion luminescence bands with maxima around 522 nm and 550 nm corresponding to the transitions from levels 2H11/2,4S3/2 and 4F9/2 to the ground state 4I15 was explained basing on two-photon processes. The measured values of fluorescence intensity ratios (FIR) were approximated by a linear function with the slopes varying from 0.0022 to 0.0039. The sample doped with 0.1 mol. % of ErF3 has the steepest inclination and the best response to temperature changes. The maximum value of absolute thermal sensitivity Smax of 69 × 10−4 °C−1 at 235 °C was obtained for the sample doped with 0.1 mol. % of ErF3. The Smax value is one of the highest values for different glass hosts found in the literature. The data obtained show that new Er3+ doped fluoroaluminate glass of the composition under investigation is a good host matrix for sensing element in optical thermometry.