High-efficiency fully concentrated Na₃Eu(VO₄)₂ phosphor with excellent thermal stability for white light-emitting diodes

In this study, fully concentrated Eu³⁺-based Na₃Eu(VO₄)₂ vanadate phosphor was synthesized by solid-state reaction process. The as-obtained product presented a single monoclinic phase with the space group of Cc (9) and rod shape with micron size, as revealed by X-ray diffraction pattern and scanning electron microscope. Their luminescence performances were investigated by the excitation and emission spectra, temperature-dependent photoluminescence spectra. At the excitation of 395 nm, they displayed a strong red emission at 620 nm and the Gd³⁺ and La³⁺ ions incorporation did not lead to luminescent quenching in this Na₃Eu(VO₄)₂ phosphor. When the temperature was as high as 420 K, the emission intensity kept 84% of the initial value at 303 K, which implied the Na₃Eu(VO₄)₂ phosphors had excellent thermal stability. Further, the activation energy (E_a) was calculated to be 0.326 eV. Meanwhile, the quantum yield of this phosphor was as high as 70.6%. Finally, by coating the mixtures of red phosphors Na₃Eu(VO₄)₂, commercial green phosphors (Sr, Ba)₂SiO₄:Eu²⁺ and blue phosphors BaMgAl₁₀O₁₇:Eu²⁺ on the surface of NUV chip (395 nm), a LED lamp was obtained and exhibited white light with good color rendering index of 93. These results exhibited the commercialized prospect of Na₃Eu(VO₄)₂ compound as a red phosphor in the field of solid-state lighting.