| In recent years,tungstate nanomaterials have paid more and more attention in electrical materials?optical materials?magnetic material?biological sensor?light-emitting diodes and other fields due to their special structural and chemical properties.AWO4:Eu3+(A=Ca,Sr,Ba)belongs to alkaline earth metal tungstate.It is one of the typical luminescent matrix materials.Europium ion is a commonly doped ion for downconversion luminescent materials.Tungstate nanomaterials doped Eu3+have excellent red light emission,good thermal stability and chemical stability,which can be used as a diode and LED white luminescent material as well as solar energy conversion materials.In this paper,three kinds of materials,hollow spherical CaWO4,dumbbell-shaped SrWO4 and jujube-shaped BaWO4,have been respectively synthesized as the main raw material of CaCl2,SrCl2,BaCl2,and Na2WO4.The optimized synthesis conditions of AW04:x%Eu3+(A=Ca,Sr,Ba),the volume ratio of ethyl alcohol to water,the doping amount of europium ion,the reaction temperature,the reaction time on the exhibit strong emission peak in the range of 612?614nm.1.Pure phase CaWO4:x%Eu3+nanocrystals were obtained at the pH value from 7 to 10.A mixture of calcium tungstate and tungstic acid was obtained at the pH range from 4 to 6.Optimum solvothermal synthesis conditions of hollow sphere CaWO4:x%Eu3+were as follows:the pH value of reaction system.The morphology of the sample was hollow ball in the radius of 0.9?1 ?m.The product have the best fluorescence properties with the Eu3+ doping content of 3%.2.Solvothermal synthesis and fluorescence properties of SrWO4:Eu3+nanocrystals with different morphologies(1)SrWO4:Eu3+ nanocrystals with various morphologies were obtained at the pH value of 5 with the ethyl alcohol and water ratio of 2:1 at the reaction temperature of 180? for different reaction time.The dumbbell-shaped SrWO4:Eu3+nanocrystals with controllable morphologies were obtained for the reaction time from 6h to 24h.The double-hemisphere dumbbell-shaped SrWO4:Eu3+nanocrystals were obtained for the reaction time of 36 h.The double crown spherical SrWO4:Eu3+nanocrystals were obtained for the reaction time of 48 h.(2)The order of the fluorescence intensity for SrWO4:Eu3+nanocrystals with different morphologies was:dumbbell-shaped>double-hemisphere dumbbell-shaped>double crown spherical.(3)The dumbbell-shaped SrWO4:Eu3+nanocrystals with Eu3+doping content of 3%have the best fluorescence properties.(4)Optimum solvothermal synthesis conditions of dumbbell-shaped SrWO4:x%Eu3+were as follows:the pH value of the reaction system is from 6h to 24h.With the Eu3+doping content of 3%,dumbbell-shaped SrWO4:Eu3+nanocrystals in a diameter of about 0.8 ?m at middle part and a length of about 2.4 ?m exhibit the best fluorescence properties.3.Optimum solvothermal synthesis conditions of jujube-shaped BaWO4:x%Eu3+were as follows:the pH value of the reaction system.When the Eu3+doping content was 3%,the obtained products with jujube-shaped,in the length of about 1.2 ?m and in the width of 0.6 ?m,have the best fluorescence performance.4.The formation mechanism of double crown spherical SrWO4:Eu3+nanocrystals was proposed.By studing the effect of the reaction time on the morphology of SrWO4:Eu3+nanocrystals,the formation mechanism of the double crown spherical SrWO4:Eu3+nanocrystals was proposed.First,the dumbbell-shaped rods were formed.With prolonging of the reaction time,the rods were gradually divergent at both ends,and the dumbbells were formed.Through dumbbell-shaped and the double hemispheres,the dumbbells were finally formed.5.Effect of the cationic radius on the fluorescence properties of AWO4:x%Eu3+(A=Ca,Sr,Ba)nanocrystals.Three kinds of AWO4:x%Eu3+(A=Ca,Sr,Ba)nanocrystals under the discussed optimal conditions were analyzed by means of XRD,energy spectra and fluorescence properties.The results show that:(1)The order of fluorescence intensity for three kinds of nanocrystals is that:CaWO4>SrWO4>BaWO4.The XRD pattern is almost the same for three kinds of nanocrystals only but the position of diffraction peak have an obvious shift,which is resulted by the difference in the radius of the alkaline earth metal ions.(2)CaWO4:Eu3+nanocrystals have the best fluorescence performance because of their smallest cationic radius and close to the Eu3+ion radius.(3)The influence regulation of the radius of alkaline earth metal on the fluorescence intensity of tungstate is that:the smaller the radius of alkaline earth metal ions is,the closer it is to the ion radius of Eu3+ions,the easier the Eu3+ions doped into the alkaline earth metal ions in the lattice are,the greater the fluorescence intensity.(4)Under the optimum Eu3+doping amount of 3%,we compared to the change(?d)of the nanocrystalline plane spacing of AWO4:x%Eu3+(M=Ca,Sr,Ba).The results we got is that Eu3+ions were mainly doped on the(101)plane of three AWO4:x%Eu3+(A=Ca,Sr,Ba)nanocrystals. |
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