Luminescence properties and energy transfers of NaLa(WO₄)₂:Sm³⁺:Ce³⁺ phosphor

A series of NaLa(WO₄)₂:Sm³⁺:Ce³⁺ phosphors are prepared by the hydrothermal method. The structure, morphology, luminescent properties of sample are characterized with X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and fluorescence spectrophotometer. The results show that all the obtained products have the scheelite structure with ellipsoidal shapes. Ce³⁺ has quenching effects on luminescence properties of NaLa(WO₄)₂:Sm³⁺ phosphors at high Ce³⁺ doping concentration. When the Ce³⁺ molar content is 1%, the intensity of the excitation and emission spectra is the maximum. It indicates that when the sensitizer Ce³⁺ has the molar content of 1%, the sensitizing ability of luminescent properties of NaLa(WO₄)₂:Sm³⁺:Ce³⁺ phosphors is the strongest. That is, Ce³⁺ can transfer energy to Sm³⁺. The critical distance of Ce³⁺ → Sm³⁺ energy transfer is 2.196 nm. The type of energy transfer of Ce³⁺ → Sm³⁺ is electric multi-pole interaction. The maximum energy transfer efficiency of Ce³⁺ → Sm³⁺ in NaLa(WO₄)₂:Sm³⁺:Ce³⁺ phosphors can reach 15.17%. The temperature-dependent emission spectra demonstrates that the NaLa(WO₄)₂: 0.02Sm³⁺:0.01Ce³⁺ phosphor has a good thermal stability with a thermal activation energy ΔE of 0.2789 eV. The CIE coordinates show that the phosphor is red, and is the potential red phosphor for LEDs.