Preparation And Luminescence Properties Of Several Oxide Phosphors For White Light-emitting Diodes

White light-emitting diodes (LEDs) technique is an important kind of solid-state illumination. In comparison with conventional incandescent and fluorescent lamps, the white LEDs show many advantages such as high luminescent efficiency, long lifetime, environment friendly, which promise significant reductions in power consumption in the 21st century. In the case of lighting, white light can be generated by several different methods. The most commonly method is to combine a phosphor with a GaN LED chip, and this is called as phosphor-conversion method. So the phosphor conversion LEDs light strongly depends on the phosphor whether it can be efficiently excited by blue or UV emission of LEDs chip or not. Now, there are two major problems on the development of phosphors:one is that the yellow phosphor used in blue LEDs has relatively weak emission in the red spectral region, resulting in inaccurate color rendition; the other is that the tricolor phosphors used in UV LEDs have a low emission intensity, resulting in a low luminous efficiency. Therefore, it is a significant work to seek a kind of phosphor with high luminous efficiency and better color reproducibility for blue or UV LEDs.The red phosphors CaMoO4:Eu3+,M(M=Si,Nb,V,Sr,Tb,Pb,etc) were synthesized by solid state reaction. We firstly found that the red emission intensity of the phosphor CaMooO4:Eu3+ was seriously enhanced when Mo6+ was replaced by Si4+ or Nb5+. The optimize emission intensity of Si and Nb co-doping samples is as 5.5 and 4 times high as that of Y2O2S:0.05Eu3+, respectively. In addition, because NaEu(MoO4)2 and CaMoO4 have similar structures, the red phosphors NaEu(Mo1-xMxO4)2 (M=Si,Nb) were also synthesized by solid state reaction. The optimize emission intensity of NaEu(Mo1-xSixO4)2 and NaEu(Mo1-xNbxO4)2 samples reached as 3.8 and 3 times as that of Y2O2S:0.05Eu3+, respectively. It indicated that the two modified red phosphors might be more suitable for the UV-LED than the sulfide phosphor Y2O2S:0.05Eu3+The phosphors YVO4:Bi3+,M3+(M=Dy,Er) were synthesized by solid state reaction, and the photoluminescence proterties under>350 nm excitation were firstly studied. Under 365 nm excitation, the sample YVO4:Bi3+,Dy3+ emitted yellow light, and the sample YVO4:Bi3+,Er3+ emitted white light. When V was replaced by P, the emission intensity of YVO4:Bi3+,Dy3+ and YVO4:Bi3+,Er3+ samples is seriously enhanced, stepping up 23% and 27% than that of original samples, respectively.The phosphors Sr1-xBaxCO3:Eu2+ were firstly synthesized by the modified solid-state reaction in a reducing atmosphere of CO/CO2 and showed excellent luminescent properties. The excitation spectra cover the range from the near-UV to the visible part, and the emission spectra show a strong emission from the orange to the red part. The results implied that the color-adjustable phosphors can match well with the blue or UV LEDs, which means that the phosphor could be regarded as a potential candidate for the phosphor-converted white LEDs.In addition, we also synthesized the titanate Y2TiO5 host phosphor and researched the photoluminescence properties.