Abstract: A series of color tunable NaCa_2-xMg₂(VO₄)₃∶xEu³⁺(0≤x≤0.10) phosphors were synthesized by molten salt method using cheap NaCl as molten salt. The effects of synthesis conditions and Eu³⁺doping on the structure and luminescence properties of the samples were investigated in details. The results show that the optimum reaction conditions for the synthesis of NaCa₂Mg₂(VO₄)₃ are reaction temperature of 800 ℃, reaction time of 0.5 h and mass ratio of raw material to molten salt of 1∶3. The obtained samples are NaCa₂Mg₂(VO₄)₃ pure phase with higher crystallinity. The micromorphology of the samples changed from coral-like to smooth irregular polyhedron with the increase of temperature. Eu³⁺ doping has little effect on the crystal structure of NaCa₂Mg₂(VO₄)₃, but great effect on its luminescence properties. With the increase of Eu³⁺ concentration (x), the characteristic emission band intensity of VO^3-₄ gradually decreases, while the characteristic emission peak intensity of Eu³⁺ first increases and then decreases, reaching the maximum when x=0.06. Therefore, the luminous color of the samples can be modulated by changing the Eu³⁺ concentration, from green to yellow-green, yellow, yellow-white and orange-red. According to the fluorescence spectrum and fluorescence lifetime analysis, it is confirmed that the energy transfer process of VO^3-₄ to Eu³⁺ exists in NaCa₂Mg₂(VO₄)₃∶Eu³⁺ phosphors, and the energy transfer efficiency is about 23%. The thermal stability analysis shows that when the temperature increases from room temperature (298.15 K) to 398.15 K, the retaining ratio of the main emission peak intensity of NaCa₂Mg_1.94(VO₄)₃∶0.06Eu³⁺ phosphor at 614 nm is 68.4%, showing its good thermal stability.

Key words: vanadate, molten salt method, luminescent property, white LED, color tunable phosphor, Eu³⁺ doping