Synthesis And Luminescence Properties Of Molybdates Red Phosphors For White Light Emitting Diodes

Since the realization of GaN-based light emitting diodes,more and more attention has been focused on whitelight-emitting LED phosphors. Whitelight-emitting LED with blue light- emitting GaNLED in combination with a yellow phosphor (YAG:Ce³⁺) result in a poor color rendering. At present, the combination of a near-UV InGaN chip （380-410 nm） with blue, green and red phosphors is another way to generate white light that will yield a high color rendering index and color reproducibility index. Both applications require red-emitting phosphors, but sofar, very limited work involving them has been reported for potential white LED applitions.Therefore, it is an attractive and challenging research task to develop novel, stable, and inorganic RE ions doped red phosphors that can be excited effectively by the near UV or blue LEDs.1. Novel red phosphors, Gd（1-x）2 （MoO₄）3: EuX³⁺（x=0.05,0.1,0.2,0.4,0.6,0.8）are synthesized through a simple coprecipitation process and characterized by using X-ray diffraction （XRD）, and fluorescent spectrophotometry.The result of XRD shows that the resultant samples areаphase. In the excitation spectra of Gd（1-X）2（MoO₄）3:Eu³⁺ phosphors,by monitoring 613 nm, the charge transfer bands（CTB） of Eu³⁺â†'O^2- and Mo⁶⁺â†'O^2- centering at around 266 and 290 nm。The characteristic red emission is also observed,ascribed to the 5D0â†'7FJ transition of Eu³⁺ions, The chromaticity coordinates of Gd₂（MoO₄）₃ are （0.64,0.35） which is very close to the NTSC standard values（x=0.67,0.33）. The optimal doping concentration of Eu³⁺ions is 60%. It is considered to be an efficient red-emitting phosphor for near UV-LED（blue） light emitting diode（LED）.2. In this paper, novel Eu³⁺-doped YMoO₄:Eux³⁺ （x=0.01, 0.05, 0.07, 0.12, 0.15, 0.2） phosphors was prepared by the co-precipitation method. The structure of sample was determined by using XRD spectrum. The emission spectra and the excitation spectra were measured and investigated. The results indicate that it is considered to be efficient red-emitting phosphors for near UV-LED （blue light）.3. Novel red phosphors,CaMoO₄:Eu0.1³⁺,Sm³⁺x（x=0,0.01,0.02,0.03,0.04,0.05,0.06,0.08）are synthesized through a simple coprecipitation process and characterized by using X-ray diffraction （XRD）, field emission scanning electron microscopy （FE-SEM） and fluorescent spectrophotometry. The chromaticity coordinates of CaMoO₄:Eu0.1³⁺phosphor and CaMoO₄:Eu0.1³⁺,Sm0.05³⁺phosphor are （0.661,0.329）and （0.667,0.328） ,But CaMoO₄:Eu0.1³⁺,Sm0.05³⁺（0.667,0.328） phosphor is very close to the NTSC standard values（x=0.67,0.33）. The optimal doping concentration of Sm³⁺ ions is 5%。The energy-transfer transition from Sm³⁺ ions to Eu³⁺ ions is demonstrated to enchance emssion of the red light by the result. It is considered to be an efficient red-emitting phosphor for near UV-LED（blue） light emitting diode（LED）.