Optical characterization of Er3+-doped zinc fluorophosphate glasses for optical temperature sensors

Trivalent erbium doped zinc fluorophosphate glasses have been synthesized and their luminescence properties in the green visible range have been investigated as a function of temperature. The Judd–Ofelt theory has been used to predict the transition probabilities, branching ratios and lifetimes for the various excited states of Er3+ ions in 0.5 mol% of Er2O3-doped glass. The effect of Er3+ concentration on temperature dependent luminescence has been studied for the wide temperature range from room temperature up to 773 K. The fluorescence intensity ratio of the green emissions associated to the two transitions from the thermally coupled 2H11/2 and 4S3/2 levels to the 4I15/2 level of Er3+ ion has been studied as a function of temperature, and in turn used to determine the thermal sensitivity and relative thermal sensitivity of the glasses. In the present study, the maximum value for the thermal sensitivity of 79 × 10−4 K−1 at 630 K has been obtained for the lowest (0.01 mol%) concentration of Er2O3-doped glass, one of the highest sensitivity found in the literature and quite close to the theoretical sensitivity calculated from the Judd–Ofelt theory. The results reveal that the zinc fluorophosphate glass having relatively low concentration of Er3+ ions can be useful as an optical temperature sensor due to their high sensitivity and the absence of radiative energy transfer processes.