Structure, energy transfer, and luminescence properties of NaLaMgWO₆: Tb³⁺,Eu³⁺ phosphors for solid-state lighting

Novel NaLaMgWO₆:Tb³⁺,Eu³⁺ phosphors with tunable color emissions were prepared by a solid-state reaction. The crystal structure, composition, and luminescent properties of the obtained phosphors were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and fluorescence spectrophotometer. The results reveal that NaLaMgWO₆ crystallizes in a monoclinic double perovskite structure with C2/m space group. Tb³⁺ and Eu³⁺ single-doped phosphors show the intense green and red emissions at 545 and 617 nm, corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ and the ⁵D₀ → ⁷F₂ transition of Eu³⁺, respectively, while for Tb³⁺ and Eu³⁺ co-doped phosphors, a tunable emission color from green to red is obtained by variation of the ratio of Eu³⁺ to Tb³⁺. The emission spectra and luminescence decay lifetimes verify the occurrence of energy transfer from Tb³⁺ to Eu³⁺ in NaLaMgWO₆: Tb³⁺, Eu³⁺ phosphor, and the energy transfer mechanism is dominated by the dipole–quadrupole interaction. Furthermore, the thermal stability of NaLaMgWO₆:Tb³⁺, Eu³⁺ phosphor was discussed from 305 to 515 K. The results exhibit the phosphors possess excellent thermal stability, and the activation energy is calculated to be 0.302 eV.