Effects of SO4(2-) or SiO3(2-) doping on the photoluminescence of NaEu(MoO4)2 nanophosphors for light-emitting diodes.

A series of red nanophosphors including NaEu(MoO4)2-x(SO4)x as well as NaEu(MoO4)2-x(SiO3)x (x = 0, 0.10, 0.20, 0.30, 0.40) were synthesized by hydrothermal and subsequent heat-treatment processes. The as-prepared pure and anion (SO4(2-) or SiO3(2-))-doped NaEu(MoO4)2 phosphors were indexed as a scheelite structure, which was revealed by X-ray diffraction data. The morphologies of SO4(2-)-doped NaEu(MoO4)2 powders were almost regularly spherical, and their grain sizes ranged from 300 to 400 nm. However, the grains of SiO3(2-)-doped phosphors appeared to be seriously inordinate and unconsolidated, as indicated by their scanning electron microscopy studies. All of the samples were excited with near-UV 395 nm light and showed the characteristic red emission of the Eu3+ 5D0 --> 7F2 transition. With the incorporation of SO4(2-) into the host, the red emission intensities of Eu3+ increased obviously and reached a maximum at x = 0.30. Nevertheless, the intensities of Eu3+ emission reduced dramatically after the SiO3(2-) doping. The optimized NaEu(MoO4)1.70(SO4)0.30 nanophosphor powders, with well-distributed fine grains and strong emission intensity, may be applied in the fabrication of phosphor-converted light-emitting diodes (LEDs).