Pr3+:LiGdF4 microparticles for optical temperature sensing

Single crystal of Pr3+:LiGdF4 (CPr = 0.01 at.%) was grown in the resistive furnace by the Bridgman-Stockbarger method. The crystal was milled in an agate mortar. The obtained powder had a tetragonal structure (88 space group I41/a). The specific heat of the sample gradually increases with the increase of temperature from 0.46 (at 200 K) to 0.62 J/g·K (at 389 K). These values are notably less in comparison to the phosphors based on LiYF4 and LiLuF4 counterparts. The luminescence spectra of Pr3+:LiGdF4 microparticles under 442 nm pulse laser excitation demonstrated temperature dependence of its shape in the 80–680 K temperature range. Specifically, the intensity of 3P1 – 3Hj emission increases in reference to 3P0 – 3Hj emission with the increase of temperature. This phenomenon was explained by the fact that 3P1 and 3P0 electron levels share their electron populations according to the Boltzmann law. The luminescence intensity ratio (LIR) was taken as a temperature-dependent parameter. The maximal absolute temperature sensitivity (Sa) was equal to 0.010 K−1 at 320 K. This value is bigger in comparison to other Pr3+ doped counterparts. The high temperature sensitivity in the 250–450 K temperature range allows using the Pr3+:LiGdF4 phosphors for biological and industrial applications. The relatively low specific heat minimizes the impact of the phosphors on the studied object for which the temperature reading is performed.