Synthesis And Luminescent Properties Of Tungstate Molybdate Phosphors For White LED Applications

The tungstates and molydateds materials have received quite a few research attentions due to their special chemical and physical properties especially for their excellent thermal stability. Therefore, they have good application prospect in the near UV excitation type LED phosphor for white LED. A series of Bi activated and Si-substituted Li Eu(Mo O4)2 red phosphors have been synthesized by sol-gel method and post-treatment such as coating silicon dioxide on the surface of the red phosphors have been adopted in order to improve the luminescence property of the red phosphor at high temperature. Moreover,single phase white light emitting phosphors Li Y(Mo O4)2:Dy, Eu have also been synthesized by changing the ratio of Dy3+and Eu3+.A series of Bi activated and Si-substituted Li Eu(Mo O4)2 red phosphors have been synthesized by sol-gel method and the luminescence properties were investigated in details. The prepared Bi activated and Si substituted Li Eu(Mo O4)2phosphor can be effectively excited by a near UV light of 395 nm and then emit red light. The positions of Eu and Si in the lattice are replaced by Bi and Si respectively. At the same time, there is a optimal value for the doping amount of Bi and Si. The best luminescence property can not be achieved if it is beyond or less. The doping samples show better luminescence properties such as quantum efficiency and lifetime because of the strong absorption capacity of Si in the near ultraviolet band and the sensitization of Bi. It is worth noting that the codoped sample Li Eu0.9(Mo0.97Si0.03O4)2 shows better property compared with the single doped sample.The Si O2 coating on Bi and Si codoped Li Eu(Mo O4)2 red phosphor were synthesized and the thermal stability of the coated red phosphor were investigated in details. The result reveals that different coating parameters contritute to the different of the size and luminescence property for the coated sample. The thermal stability of the red phosphor after coating is enhanced greatly compared with the uncoated sample.The single phase tungstates and molybdates white light emitting phosphors of Li Y(Mo O4)2:Dy3+, Eu3+were synthesized by sol-gel method. We haveanalyzed the effects of different process parameters such as p H and the amount of citric acid on the structure and photoluminescence properties of the phosphor.At the same time, the influences of the ratio of Mo and W on the luminescence property were also discussed. The optimal doping amount of Dy3+is obtained by adjusting the amount of Dy3+. Based on the above investigations, the single phase tungstates and molybdates white light emitting phosphors Li Y(Mo O4)2:Dy3+,Eu3+ are obtained by adjusting the doping amount of Eu3+.