Effects of Er3+ concentration on thermal sensitivity in optical temperature fluorotellurite glass sensors

The effects of Er3+ concentration on temperature-dependent luminescence in fluorotellurite glass were studied in the 100–573 K range for its application as an optical temperature sensor. The temperature-induced changes in the Er3+ green emissions associated to the transitions from the 2H11/2 and 4S3/2 thermalized levels to the 4I15/2 ground state were calibrated by doping the fluorotellurite glasses with three concentrations (0.01, 0.1 and 2.5 mol% of Er3+ ions) and using commercial cw 488 nm laser excitation. The intensities, quantum efficiencies, line profiles and fluorescence intensity ratio of these thermalized green emitting levels are highly dependent on the optically active Er3+ concentration and the position of the glass excited by the laser beam due to the existence of radiative and non-radiative energy transfer processes between Er3+ ions. The maximum value for thermal sensitivity were obtained for the fluorotellurite glass doped with the lowest concentration of Er3+ ions, 79 × 10−4 K−1 at 541 K, one of the highest values found in the literature, and quite close to the theoretical thermal sensitivity calculated using the Judd–Ofelt theory. This study concludes that the calibration of optical temperature sensors based on Er3+ ions is strongly affected by radiative energy transfer processes, therefore a relatively low concentration of Er3+ ions should be used to avoid them.