Rare Earth Europium Doped Tungsten/molybdate Red Light-emitting Materials Preparation And Performance Of The Research

The white LED is a new type of solid state lighting with many advantages and wide range ofprospects for use. In order to meet the requirements of the development of white LED devices, itis urgent need to develop new luminescent materials with stable performance, green and efficient,suitable for near ultraviolet LED excitation. Tungstates/molybdates have a good chemical stabilityand thermal stability as matrix material. Now mainly luminescent materials were using thetraditional high temperature solid-state to prepare, but this synthesis need high temperature, highenergy consumption. Therefore, the paper have adopted the low-power soft-chemical methods tosynthesize different morphologies and particle size of rare earth doped tungstates/molybdatesluminescent materials, by controlling the synthesis conditions, and its luminescent properties havebeen investigated.KGW:Eu red phosphor was prepared by sol-gel method. The effect of changing sinteringtemperature and Eu³⁺doping concentration on luminescence has been studied. The result showthat the samples crystallinity prepared by sol-gel method become better than those of hightemperature solid-state method, shape are more regular, and the luminous intensity are higher. Theaverage particle size is2.25±0.75μm. These phosphors’ strongest excitation peak （395nm） locatesin the UV-LED chip （InGaN light-emitting diode） emission wavelength range. KGW:Eu phosphoremits strong red light by395nm excitated. Therefore the optimum mole content of Eu³⁺inphosphors is40mol%and optimum calcination temperature is950℃.NGW:Eu nanocrystals were prepared successfully by the mild hydrothermal method （thehydrothermal conditions: pH=7,240°C,10h）. The emission spectra of NGW:Eu phosphor in thenear-UV （395nm） excitation can emit bright red light （615nm）, corresponding to the⁵D₀â†'⁷F₂transition. The⁵D₀â†'⁷F₂transition possesses a single emission peak, and fluorescence decay curveof5D0energy level can be fitting by single-exponential curve, indicating that Eu³⁺ion lies in thelattice environment with only one symmetry site. Eu³⁺optimum doping concentration is about60at.%.LLM:Eu phosphors of different Eu³⁺ions doping concentration prepared by sol-gel method.By thermogravimetry-differential thermal analysis, it is indicated that the phosphor wascrystallization very well at900°C. The structure and morphology of the sample and itsluminescent properties have been investigated in-depth. The strongest excitation peak （395nm）matches with the emission wavelength of commercially available UV-LED chips. The emissionspectra show that LLM:Eu phosphor at616nm have an intense emission, which is correspondingto the⁵D₀â†'⁷F₂transition, and emits strong red light. Indicating that the Eu³⁺ions in the the LLMcrystal environment is inversion symmetry. The optimum doping concentration of LLM:Euphosphor is55at.%, quantum efficiency is68%.The rare earth heteropoly tungstic acid luminescence materials of K_11-xCs_xRE(PW₁₁O₃₉)₂（RE=Eu, Sm, Dy, Gd） were synthesised by solution method. Among of them, theK_11-xCs_xGd(PW₁₁O₃₉)₂crystal have no luminescence. K_11-xCs_xSm(PW₁₁O₃₉)₂luminescencematerials emits strong orange light （598.7nm）, under395nm excitation. K_11-xCs_xDy(PW₁₁O₃₉)₂luminescence materials have two strong emission peaks, about479nm with blue light and about574nm with yellow light, respectively. Two types of mixed light produced white light. Emissionspectra of K_11-xCs_xEu(PW₁₁O₃₉)₂crystal showed that there exist strong red light at614,702nm,which correspond to⁵D₀â†'⁷F₂,⁵D₀â†'⁷F₄transition, respectively. excitation spectra of threecrystals K_11-xCs_xRE(PW₁₁O₃₉)₂（RE=Eu, Sm, Dy） showed that the strongest peak match well withcommercial UV-LED chips.