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In this work, the physical characterization of LiGdxY1−xF4 (x = 0.05, 0.3, 0.7, and 1.0) and LiGdF4:Eu3+ microparticles was performed. The distribution coefficient of LiGdxY1−xF4 (x = 0.05) was determined for the first time (0.84). Based on kinetic characterization data, the LiGdF4 sample was chosen for further Eu3+ doping (0.1 and 1.0 at.%). For the LiGdF4:Eu3+ sample, Eu3+ emission was clearly observed under the excitation of Gd3+. This fact indicates an effective energy transfer from Gd3+ to Eu3+. The temperature-dependent spectral characterization of the LiGdF4:Eu3+ (1.0%) sample revealed that in the 30–250 K temperature range, a broad emission peak is evidenced. Its intensity sharply increases with the temperature decrease. We made a suggestion that this phenomenon is related to the irradiation-induced defects. The integrated luminescence intensity ratio of this broad peak and the Eu3+ emission were taken as temperature-dependent parameters. The sensitivity values are very competitive, and the first maximum occurs at 174 K (3.18%/K). The kinetic characteristics of both Gd3+ and Eu3+ did not demonstrate a notable temperature dependence. The LiGdF4:Eu3+ sample showed the possibility of being used as an optical temperature sensor, operating in the cryogenic temperature range.

Calcium sulfate powder materials containing terbium ions at 0, 1.0, or 2.0 mol.% were obtained. They are characterized by the presence of a CaSO4 × 0.5H2O phase, while Tb3+ is incorporated into the lattice at ≤1.0 mol.%. Specific surface area enlarged from 2.1 to 22.5 m2/g as crystallite size decreased from 68 to 31 nm. Thermal analysis showed that terbium slightly raises the temperature of CaSO4 × 2H2O-to-CaSO4 transition. Studies of solubility in SBF solution showed the presence of a calcium phosphate layer in terbium-containing cements on the 7th day. Luminescent properties were studied by excitation at 266 nm and 489 nm corresponding to absorption bands of the host and Tb3+ (7F6 - 5D4 absorption band). The recorded emission peaks of the materials showed that the luminescence of the samples was green, with the luminescence intensity increasing when Tb3+ was introduced. The developed materials can find applications in medicine as bioimplants with a possibility of noninvasive visualization of the bone restoration process.

YF3: (Eu3+, Nd3+) nanoparticles (orthorhombic phase, D~130 nm) were synthesized via the co-precipitation method, with subsequent hydrothermal treatment and annealing. The Eu3+ τdecay linearly descends with the increase of temperature in the 80–320 K range. The τdecay (T) slope values of the annealed YF3: Eu3+ (2.5 and 5.0 mol.%) nanoparticles were the highest (110·10−4 and 67·10−4, μs/K) in the whole 80–320 K range, respectively. Thus, these samples were chosen for further doping with Nd3+. The maximum Sa and Sr values based on the LIR (IEu/INd) function were 0.067 K−1 (at 80 K) and 0.86%·K−1 (at 154 K), respectively. As mentioned above, the single-doped YF3: Eu3+ (2.5%) nanoparticles showed the linearly decreasing τdecay (T) function (5D0–7F1 emission). The main idea of Nd3+ co-doping was to increase this slope value (as well as the sensitivity) by increasing the rate of τdecay (T) descent via the addition of one more temperature-dependent channel of 5D0 excited state depopulation. Indeed, we managed to increase the slope (Sa) to 180·10−4 K−1 at 80 K. This result is one of the highest compared to the world analogs.