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.

Herein, we report a case of A₂MgWO₆ (A = Ca, Sr, Ba) doped with 2%Dy³⁺, 2%Li⁺, in which the influences of the cation substitution are exhibited through the crystal structure, the charge transfer band (O^2--W⁶⁺), the emission spectrum, the color of the luminescence, and the luminescent decay time. The substitution of Ca²⁺ and Sr²⁺ ions for larger ions (Ba²⁺) led to the crystal structure alteration from cubic to monoclinic and tetragonal, respectively. These structure changes also lowered the crystallography symmetry site of Dy³⁺, tuned the color of the emitted light from the whitish to yellowish region, and caused a blue shift of the CTB. Furthermore, a significant decline in the lifetime of the ⁴F_9/2 → ⁶H_13/2,15/2 transitions was noticed, from 748, 199, to 146 μs corresponding to Ba, Sr, Ca sample owing to the reduction in the local symmetry of Dy³⁺. Moreover, the thermal sensing properties of 2%Dy³⁺-doped samples were investigated based on the fluorescence intensity ratio technique in the range of 80-325 K. Under 266 nm excitation wavelength, the maximum relative sensitivity of the investigated samples was remarkably enhanced from 2.26%/K, 3.04%/K, to 4.38%/K corresponding to Ba, Ca, and Sr samples, respectively. In addition to providing a comprehensive understanding of the effects of compositional modifications on the optical properties, the results also present a viable pathway to manipulate the temperature sensing performance.

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.

A bifunctional luminescent material is one of the most intriguing topics in recent years with significant growth in the number of investigations. Herein, we report the potential of Ba₂MgWO₆ doped with Er³⁺ as a candidate for white-light emitting phosphor and noncontact luminescent thermometry. The synthesis of the samples was carried out by the co-precipitation method. The influence of the dopant concentration on the emission intensity, as well as the capability of temperature readout, was investigated for the first time. The highest emission intensity exhibits a sample comprising 4% Er³⁺; above it, the concentration quenching process by the dipole–dipole interaction occurs. However, high quality white light generates Ba₂MgWO₆ with 0.5% of Er³⁺ due to the coexistence of the host and erbium ion emission with a CIE of (0.30, 0.35). To construct a non-contact luminescent thermometer based on Er³⁺, the ratio of the emission from ⁴I_11/2 → ⁴I_15/2 to the host emission was examined. The highest sensitivity S_r of the obtained luminescent thermometers was 2.78% K⁻¹ at 198 K. The repeatability of the calculated results and the uncertainty δT of the temperature readout were investigated.

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.