Study On Preparation And Luminescence Properties Of Rare Earth Doping Tungsten Silicate Glass-Ceramic

The tungsten ions with the larger electronegativity can capture the free oxygen to form [WO₄]2-tetrahedral units.The crystallization stability of glass can be improved because the [WO₄]2-tetrahedral unitsparticipate in the construction of three-dimensional network of glass,which enhances the tightness of the glass network structure and the viscosity of glass.The luminescence spectrum of tungstate is very stable and the intrinsic luminescence spectrum is very wide.The intrinsic luminescence center of the tungstate is [WO₄]2-,and the position of the emission band is strongly affected by the cation of the tungstate.Tungstate phosphor is the typical self activated luminescence materials,also can be activated by rare earth ions.These rare earth ions enter into the tungstate lattice and their luminescence efficiency improved significantly because there is an energy transfer between them and the W-O bonds.In this thesis,preparation and the luminescence properties of transparent glass ceramics containing tungsten were studied.The glass ceramics containing CaWO₄,ZnWO₄ and NaY?WO₄?2 were prepared and the optimum heat treatment schedule was determined.Er³⁺-Yb³⁺,Tb³⁺ and Eu³⁺ doped into glass ceramics containing Ca WO₄,Zn WO₄ and Na Y?WO₄?2,the influence rare earth ions on crystal structure of the crystallization phase was investigated and the luminescence properties of these rare earth ions were compared.The crystal structure of Ca WO₄ and Na Y?WO₄?2 is more stable,and the doping of rare earth ions does not change the crystal phase of the glass ceramics.Zn WO₄ is an unstable structure of wolframite.The crystal phase transform from Zn WO₄ to Na0.5Re0.5WO₄?Re: Er,Yb,Tb,Eu?with the increasing of doping concentration of rare earth ions.The rare earth doped tungsten silicate glass ceramics show excellent luminescent properties,and the best doping concentration of rare earth ions were determined.The relationship between the microstructure and the optical transmittance of tungsten silicate glass ceramics was studied by the principle of stereology.The volume fraction of the grains decreases and the optical transmittance increases with the increasing of the three-dimensional free distance.With the increase of the three-dimensional sphere diameter,the optical transmittance decreases,so the grain size should be controlled to improve the optical transmittance of the glass ceramic samples.With the increasing of the average specific area of the single crystalline grain,the transmittance increases in the unit volume.The results indicate that the optical transmittance of the samples decreases with the increasing of the grains size in the glass ceramics and more complex the morphology.IR and Raman spectra was used to study the microstructure of tungsten silicate glass ceramics.The results show that the network structure of the residual glass phase in the three systems mainly is Q2,Q3 and [BO₃].The Raman spectra of the glass ceramic samples with different heat treatment systems were analyzed by fitting,and the effect of the crystallization on the relative unit of the glassceramics network was studied.With the increasing of tungstate crystal,the diffraction peaks of Si-O-M,B-O-M?M=Ca,Zn,Na,W?bandgradually weakened.The Er³⁺: NWO₄?N=Ca,Zn?tungsten silicate glass ceramics were studied according to the crystal field theory.The crystal field parameter value were calculated by the superposition model on the basis of the analysis of the structure of NWO₄.Combining the fitting between the ion parameter and the spectra,compared with experimental spectra,the error of the accuracy root-mean-square was estimated to be ??Ca?=11.6cm-1,??Zn?=14.26cm-1,which indicate the fitting of levels were better.The crystal field parameters are obtained by fitting the energy level,and the crystal field strength?N? = 2163.8cm-1?is calculated.It shows that the calculation of crystal field parameters and the fitting of the energy level by using the superposition model is feasible.It can also be used to explain the energy level splitting and shift in the spectra of rare earth doped glass ceramics,and to compare the luminescence efficiency of rare earth ions in different crystal phases.