Controllable Synthesis of NaLu(WO₄)₂:Eu³⁺ Microcrystal and Luminescence Properties for LEDs

The phosphors of trivalent rare-earth ion Eu3+-activated alkaline double tungstates NaLu­(WO4)2 were prepared by the EDTA-assisted hydrothermal method. The crystal structure and morphology of the as-synthesized phosphors were determined by powder X-ray diffraction (XRD) and electron microscopes (SEM and TEM), respectively. The phase and morphology can be controlled by different Eu3+-doping concentrations. Not less than 40 at % of Eu3+ doping concentration pledged the NaLu­(WO4)2:Eu3+ structure, and the microcrystal changed from hexahedron to tetrahedron with increasing Eu3+ doping concentration. It was found that the final product of NaLu1–xEux(WO4)2 (x ≥ 0.4) can not be obtained directly, intermediated by WO3, Na2W2O7, and REO­(OH). The photoluminescence and electroluminescence properties were also investigated. Because of an intense red emission and a good excitation in the region of near-ultraviolet (n-UV), the samples NaLu­(WO4)2:Eu3+ can be served as alternative red phosphors in the n-UV chip-based LED application.