Relevance of radiative transfer processes on Nd3+ doped phosphate glasses for temperature sensing by means of the fluorescence intensity ratio technique

We analyze the suitability of Nd3+ doped phosphate glasses as optical temperature sensors based on the response of their luminescence bands to temperature. At room temperature, laser excitation of the sample at 532 nm results in an emission spectrum with an intense band centered at 880 nm and an adjacent weak broad band centered at 810 nm, corresponding to the Nd3+ ion transitions: 4F3/2 → 4I9/2 and 4F5/2 → 4I9/2 respectively. Because of thermalization effects between the next 4F3/2 and 4F5/2 energy levels (ΔE ≈ 908 cm−1), a detectable change on the relative intensities of these emission bands occurs when temperature is increased, affording the experimental calibration of the fluorescence intensity ratio with temperature in the range 300-850 K. It has been shown that the radiative transfer processes favored by the content of Nd3+ ions are also responsible for changes to the spectra shapes and so play an important role in the fluorescence intensity ratio. A reliable thermal sensing operation was obtained in a 0.1 mol% doped Nd3+ phosphate glass with relative sensitivity values ranging from 153 × 10−4 K−1 at 300 K to 22 × 10−4 K−1 for 850 K, demonstrating good prospects for optical temperature measurements compared to other reported results. However, the reabsorption measurements seen in the samples with a higher Nd3+ content reveal that the reliability of the sensing performance is compromised with the doping concentration and the experimental conditions of the measurement.