Synthesis, energy transfer mechanism, and tunable emissions of novel Na₃La(VO₄)₂:Re³⁺ (Re³⁺ = Dy³⁺, Eu³⁺, and Sm³⁺) vanadate phosphors for near-UV-excited white LEDs

In this study, novel Eu³⁺-, Dy³⁺-, and Sm³⁺-activated Na₃La(VO₄)₂ phosphors were synthesized using a solid state reaction method. X-ray diffraction analysis results indicated that the Na₃La(VO₄)₂ phosphors had an orthorhombic crystal structure with the Pbc21 space group. There were two different La(1)O₈ and La(2)O₈ polyhedra with high asymmetry in the crystal structure. Scanning electron microscopy revealed that the product had a sheet morphology with an irregular particle size. Further, the luminescence properties, including the excitation and emission spectra, and luminescence decay curve, were investigated using a fluorescence spectrometer. The results showed that the Na₃La(VO₄)₂ compound was an excellent host for activating the luminescence of Eu³⁺ (614 nm), Dy³⁺ (575 nm), and Sm³⁺ (647 nm) ions. Further, Dy³⁺/Eu³⁺ co-doped Na₃La(VO₄)₂ phosphors were exploited, and the energy transfer from Dy³⁺ to Eu³⁺ was demonstrated in detail by the photoluminescence excitation, photoluminescence spectra, and luminescent decay curves. The results showed that the energy transfer efficiency from Dy³⁺ to Eu³⁺ was highly efficient, and the energy transfer mechanism was dipole–dipole interactions. Finally, tunable emissions from the yellow region of CIE (0.3925, 0.4243) to the red region of CIE (0.6345, 0.3354) could be realized by rationally controlling the Dy³⁺/Eu³⁺ concentration ratio. These phosphors may be promising materials for the development of solid-state lighting and display systems.