| Tungstate was regarded as a potential luminescent material that dued to its high chemical stability,high average refractive index,high X-ray absorption coefficient,high light efficiency,short decay time and low afterglow luminescence,therefore,it is applied to new materials of microwave radiation laser emission,fluorescent materials and optical burning lattice materials.ZnWO4 host is considered as a potential phosphor matrix material because of its special wolframite oblique crystal structure,which provides a good space occupying environment for rare earth ions doping.The ZnWO4:Eu3+ phosphors have been prepared by molten salt in this work.The phase structure compositions,morphologies,selective electron diffraction pattern and lattice fringe,surface scanning of elements,vibration mode,absorption rate,fluorescent properties,quantum yield and thennal stability of as-obtained sample were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),high-resolution electron scanning electron microscopy(HR-TEM),energy spectrum analysis(EDS),Raman spectroscopy(Raman),UV-Vis absorption spectroscopy,fluorescence spectroscopy(PL),fluorescent efficiency testing system and thermal stability spectrometer,respectively.The research contents and solutions of this paper are as follows:(1)In order to study the morphology of phosphors.In this work,the effects of process parameters on the phase and crystal morphology of ZnWO4 were studied.The research have indicated that the powder particles were synthesized under the composite salt environment of LiNO3-NaNO3,NaCl-KCl,LiNO3-NaCl,LiNO3-KNO3,Na2WO4-KCl and KNO3-NaNO3 have relatively uniform particle morphologies and good particle dispersion.Moreover,the powder particles were synthesized under the composite salt environment of LiNO3-NaNO3 also have different particle morphologies under different annealing temperatures.Under the environment of LiNO3-NaNO3 compound molten salt,the morphologies were well developed,and the rod-like particles with regular morphologies were obtained at 180? annealing temperature.As the temperature gradually increased,finally the rod-like particles developed into the flake-like morphology.It was found that the material ratio was 1:4,that is,optimum molar ratio of the total mass of reactants to the content of molten salt was 1:4.In this process,the ZnWO4:Eu3+ phosphors were prepared with two diverse morphologies.Under the condition of determining the composition of molten salt,the content of molten salt and annealing temperature,the rod-like ZnWO4:0.07Eu3+ phosphors with small particles can be prepared at 180?,and reaction time for 8 h.The flake-like ZnWO4:Eu3+ red phosphors were synthesized in the annealing temperature was 200? and the reaction time was 10 h.(2)The impact of the doping concentration of Eu3+ ions on the luminescent properties,quantum yield and thermal stability of ZnWO4:Eu3+ phosphors were studied.Red phosphors with diverse morphologies were synthesized,both of which were optically pure monoclinic wolframite structure,and both were polycrystalline structures.The results showed that the morphology of the rod-like particles had better development,flourescent intensity,longevity,color coordinates,relative color temperature and color purity value.Excited by near-ultraviolet light with a wavelength of 394 nm,the longevity of rod-like phosphors is 0.68 ms,the CIE coordinate is(0.6301,0.3640),the value of correlated color temperature is 2076 K,the value of color purity is up to 85.3%.The rod-like morphology of ZnWO4:0.07Eu3+ phosphors were synthesized,at the same time,the concentration change of Eu3+ ions was studied.It was found that the phase transition of the synthesized ZnWO4 appeared after the Eu3+concentration exceeded 0.07 mol.Therefore,we chose the Eu concentration of 0.07 mol as the optimal doping concentration.The quantum yield of rod-like ZnWO4:0.07Eu3+ phosphors were 40.5%.Compared with CaGd4F14:Ce3+phosphors and Y2MoSiO8:Eu3+ phosphors,the thermal stability of ZnWO4:0.07Eu3+ phosphors were better.The activation energy of the two phosphors were 0.503 eV and 0.29 eV,respectively.The activation energy of the ZnWO4:0.07Eu3+ phosphors were 0.578 eV.It is concluded that rod-like ZnWO4:0.07Eu3+ red phosphors have great potential in the field of LED.(3)The structure refinement of ZnWO4 host and ZnWO4:Eu3+ red phosphor was studied.The ZnWO4 host and ZnWO4:0.07Eu3+ phosphors crystal structure were confirmed the wolframite crystal structure,crystal structure parameters were a=4.686 A,b=5.706 A,v=132.305 A3,a=4.687 A,b=5.721 A,c=4.937 A,v=132.380 A3.Through VESTA and Findit software were used to construct the crystal structure.The bond lengths and bond angles of the hexahedral[ZnO6]and hexahedron[WO6]clusters were obtained.By using VESTA software draw crystal structure diagram,slight structural changes were found,indicating that the rare earth Eu3+ ions doping can result in slight distortion in the crystal structure of ZnWO4.(4)The impact of the doping concentration of Er3+ ions on the surface valence and chemical composition and J-O analysis of ZnWO4:Eu3+ phosphors were studied.The chemical composition and valence of elements were analyzed by XPS.From the above analysis,confirming that the valence states of C,Zn,W,O and Eu are 0,+2,+6,-2 and+3,respectively.The symmetric properties of the ZnWO4:0.07Eu3+ phosphors crystal environment were calculated by J-O theory,the transition strength parameters of the ZnWO4:0.07Eu3+phosphors(?2,?4,?6),magnetic dipole transition ratio AR(md)and the electric dipole transition ratio AR(ed),radiative transition lonevity ?R and fluorescence branching ratios ?j were obtained.The stability of Eu3+ crystal environment can be determined by the relationship between ?2 and ?4,and ??eff,?e and ?eŚ??eff were calculated the parameter of ZnWO4:0.07Eu3+ phosphors,which shows the relationship between excited cross-sectional area and gain are related.With the larger of the excited cross-sectional area,the laser performance of the laser device were better. |
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