Preparation and photoluminescence properties of Eu³⁺ ion-doped Mg₂LaTaO₆ phosphor

The luminescent properties of Eu³⁺ ion-doped Mg₂LaTaO₄ phosphors were synthesized using a vibrating milled solid-state reaction. The XRD results show that the crystal structure of the Mg₂LaTaO₄:Eu³⁺ phosphor that is calcined at 1450 °C for 8 h has a cubic structure and the (440) diffraction peak shifts to a higher diffraction angle when the Eu³⁺ ion concentration increases. The absorption spectra results show that the absorption band d in the range 190–400 nm is attributed to absorption of pure Mg₂LaTaO₄ by the host lattice. When Mg₂LaTaO₄ is doped with Eu³⁺ ions, the broad band that is centered at 295 nm is assigned to the charge transition state (CTS) for the interaction of O²⁻ and Eu³⁺ with the Mg₂LaTaO₄ host lattice. The sharp peaks from 310 to 550 nm are attributed to the typical intra-4f transitions of Eu³⁺ ions. When the phosphor is excited using either 393 or 464 nm there is a red emission at 605 nm that is attributed to the electric dipole transition (⁵D₀ → ⁷F₂) for the Eu³⁺ ion. The asymmetry ratio is about 2–2.5, which lies well within the range of usual values for oxide glasses, which demonstrates that the Eu³⁺ ions occupy low-symmetry sites. The maximum intensity of the photoluminescence for the ⁵D₀ → ⁷F₂ transition occurs at an Eu³⁺ ion concentration of 30 mol%, which demonstrates that there is concentration quenching at higher Eu³⁺ concentrations. The critical distance is about 7.68 Å for the ⁵D₀ (J = 3, 2, 1) transition and the energy transfer is characterized as a wave-function exchange.