Preparation And Luminescence Properties Of NaGd（WO₄）₂:Eu³⁺ Phosphor For WhiteLEDs

White light emitting diodes (WLEDs) are considered to be the next generation lighting systems because of advantages such as low power consumption, high efficiency, long lifetime, and lack of toxic mercury compared to conventional light bulbs. At present, phosphor-converted white LEDs are the main methods to obtain white LEDs. The white light must include red light composition in order to improve the quality of white light, so red phosphors play an important role in the white LED. Red phosphors are mainly made of sulphides and oxysulfides. Because they have low luminescence efficiency and less chemical stable, and it has become the one of restraining factors. Aiming at the above state, the NaGd (WO4)2:Eu3+ materials doped by rare earth ions were synthesized by solid state reaction and sol-gel method, respectively, and the relations between the powders synhesis processing, microstructure and luminescence properties were discussed.A series of NaGd1-x(WO4)2:Eu3+x(x=0.05,0.1,0.15,0.2,0.25,0.3) red phosphors have been synthesized by solid state reaction. The crystal structure and spectral characteristics of the samples in the different calcination temperature were investigated by the X-ray diffraction (XRD), scanning electron microscope (SEM) and fluorescence spectrophotometer(PL). The results show that the pure tetragonal phase NaGd (WO4)2 with sheelite structure can be obtained at 900 ℃. In the fluorescence spectra of NaGd (WO4)2:Eu3+, it is found that NaGd (WO4)2:Eu3+ phosphors can be effectively excited by near-UV (393 nm) and blue light (464 nm), the main peaks are located at about 592 nm and 615 nm due to the 5Doâ†'7F2 and 5Doâ†'7F2 transition of Eu3+ ions, respectively. The effect of calcined temperatures and doping concentration of Eu3+on the PL intensities of NaGd (WO4)2:Eu3+ have been discussed. The results indicate that the luminescent intensity of the samples increase first and then decrease with the increasing of the calcined temperature and doping concentration of Eu3+ ions, and then get optimal synthetic condition is 25 mol% at 1000 ℃.A series of NaGd0.75-x(WO4)2:Eu3+025 Bi3+x and NaGdo.75-x(W04)2:Eu3+0.25 Sm3+X red phosphors were synthesized by solid state reaction. This paper is mainly concerned with the effect of sensitizer Bi3+ and Sm3+ ions on the NaGd0.75-x(W04)2:Eu3+0.25 phosphors’s structure and luminescence properties. The study found that the doping of Bi3+ and Sm3+ didin’t change the crystal structure of NaGd0.75(WO4)2:Eu3+0.25-However, under UV excitation, its luminous intensity vary with the change of the concentration of Bi3+ and Sm3+ ions due to energy transfer between Bi3+,Sm3+ and Eu3+. The best doping concentrations of Bi3+ and Sm3+ ions are 4 mol% and 1 mol%, respectively.Finally, the effect from sintering temperature and doping concentration of Eu3+ ions on the emission property of NaGd1-x(WO4)2:Eu3+x phosphor synthesized by sol-gel method was studied. The results showed that the optimum sintering temperature and the concentration of Eu3+ ions were 900 ℃ and 25 mol%, respectively. At last, compared to the two samples with solid state reaction and sol-gel methods respectively, the sample prepared with solid state reaction method is superior to the sample synthesized by sol-gel method in terms of luminescence property.