Eu³⁺ doped Ba₂MgWO₆ (BMW) double-perovskite was successfully synthesized for the first time by the co-precipitation method. The synthesis procedure, crystal structure, as well as morphology of obtained samples are presented. Domination of the ⁵D₀–⁷F₁ magnetic–dipole over forced electric–dipole transitions in the emission spectra indicates that Eu³⁺ ions are located in the high symmetry site with inversion center. Only one emission line assigned to the ⁵D₀–⁷F₀ transition was observed, confirming that europium substituted for only one host cation site. The photoluminescence excitation (PLE) spectrum is dominated by a strong and broad band related to the O²⁻ → Eu³⁺ and O²⁻ → W⁶⁺ charge transfer. The decay of the emission from the ⁵D₀ and ⁵D₁ levels was investigated. The temperature-dependent emission spectra showed that the T_0.5 is equal to 350 K. Extinguishing mechanisms of the Eu³⁺ luminescence in the studied host are discussed.

To fulfil the requirements of operating at low temperature in a harsh environment, the investigation on optical thermometers plays an increasingly important role. In this work, the influence of vanadium concentration on the capability of temperature readout by La₂MgTiO₆:V⁵⁺,Cr³⁺ luminescent thermometers was investigated for the first time. The presence of V³⁺ and V⁵⁺ was verified by XPS and absorption measurements. In the emission spectra, a blue–green emission region was assigned to both host and V⁵⁺ emission. Moreover, a spin-forbidden emission of Cr³⁺ ions was also detected. Vanadium ions in the +3 oxidation state do not exhibit luminescence, but play a role as a charge compensator. The highest emission intensity was obtained from the sample doped with 0.1% V. Besides, with increasing vanadium concentration, a redshift in the maximum position of the spectrum was observed corresponding to a movement from the greenish blue to yellowish green region in the CIE1931. It was shown that the relative sensitivity (S_r) and the temperature operating range can be easily modified by changing the concentration of vanadium ions. In particular, the outstanding relative sensitivities of 1.71% K⁻¹ (at 187 K) and 1.96% K⁻¹ (at 165 K) obtained from La₂MgTiO₆:0.1%V⁵⁺,Cr³⁺ and La₂MgTiO₆:0.05%V⁵⁺,Cr³⁺ demonstrated the enormous potential of this material for thermal sensing application.

In this paper, the structural, thermal, optical, and spectroscopic properties of Er³⁺‐doped tellurite glasses with the composition 68.25TeO₂–19.5ZnO–9.75X–2.5Er₂O₃(in mol%) with X = BaO, Na₂O, and Bi₂O₃are reported. The glasses were prepared using the standard melt quenching method. The investigated glasses exhibit low phonon energy (∼745 cm⁻¹) and low glass transition temperature varying between 300 and 350°C depending on the glass composition. The Raman spectra show a regular tellurite structure with variations in the number of bridging and non‐bridging oxygens depending on the glass composition, the Na₂O and Bi₂O₃‐containing glasses having the most and the least polymerized network, respectively. A thermal treatment of the glasses leads to the formation of crystals, the composition of which depends on the glass composition, as revealed by X‐ray diffraction analysis and confirmed using scanning electron microscope‐energy‐dispersive spectroscopy. The precipitation of Er‐containing crystals in the Na₂O and BaO‐containing glasses leads to an increase in the intensity of the upconversion emissions. Although the Er³⁺ions remain in the amorphous part of the Bi₂O₃‐containing glass after heat treatment, it is the precipitation of Bi_3.2Te_0.8O_6.4crystals in this glass, which is thought to decrease the distance between the Er³⁺ions leading to an increase in the intensity of the upconversion and mid‐infrared emissions.

This work aimed to explore the temperature-sensing performance of La₂MgTiO₆:Er³⁺ double perovskites based on thermally coupled and uncoupled energy levels. Furthermore, the crystal structure, chemical composition, and morphology of the samples were investigated by powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy, respectively. The most intense luminescence was observed for the sample doped with 5% Er³⁺. The temperature-dependent emission spectra of La₂MgTiO₆:5% Er³⁺ were investigated in the wide range of 77–398 K. The highest sensitivity of the sample was equal to 2.98%/K corresponding to the thermally coupled energy level ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 as compared to 1.9%/K, obtained for the uncoupled energy level ²H_11/2 → ⁴I_15/2 and ²H_9/2 → ⁴I_15/2. Furthermore, the 300 K luminescent decay profiles were analyzed using the Inokuti–Hirayama model. The energy transfer among Er³⁺ ions was mainly regulated by the dipole–dipole mechanism. The critical transfer distance R₀, critical concentration C₀, energy transfer parameter C_da, and energy transfer probability W_da were 9.81 Å, $2.53\times {10}^{20}$ ions·cm⁻³, $5.38\times {10}^{-39}$cm⁶·s⁻¹, and 6020 s⁻¹, respectively.