Preparation And Luminescence Properties Of Rare Earth Doped Tellurite Phosphor

Among rare earth doped luminescent materials,oxide substrates can meet the use of various application conditions,such as high temperature,humidity and corrosive environments,due to their advantages of simple synthesis process and good stability,thus having potential applications in lighting and display,solar cells,optical temperature sensing,etc.There are numerous techniques to synthesize rare earth doped luminescent materials,among which the wet chemical method has many advantages.In this thesis,a series of Yb³⁺/Er³⁺co-doped,Tb³⁺,Dy³⁺,Eu³⁺mono-doped and Tb³⁺/Dy³⁺/Eu³⁺ions co-doped phosphor materials were prepared by hydrothermal method using Gd₂Te₄O₁₁（GTO）as the substrate material.The effects of various pH on the material morphology and luminescence properties were examined.The energy transfer process between rare earth ions was discussed exhaustively by changing the doping concentrations of rare earth ions.The primary substance of this article is as per the following:（1）Gd₂Te₄O₁₁:Yb³⁺/Er³⁺up-conversion phosphor was synthesized in one step by hydrothermal method.The effects of various pH and rare earth ions concentrations on the phase,morphology and radiance of the samples were discussed.The results include:（1）We obtained stable crystal structures even if x%Yb³⁺and y%Er³⁺（x=0-20,y=0.25-3）are added into GTO matrix.By optimizing the concentration of Yb³⁺and Er³⁺,the brightest green luminescence was obtained under the excitation of 980 nm laser when the concentration ratio of Yb³⁺and Er³⁺was 15:1.（2）The pH of the aqueous phase of the reactants was gradually increased from acidic（pH（?）1）to alkaline（pH（?）9）under a doping ratio of Yb³⁺,Er³⁺concentration at 15:1,and it was found that the materials did not obtain the crystal phase under alkaline conditions.In addition,up-conversion luminescence of the materials first increase and then decrease,with the strongest green emission at pH（?）5.（2）Carrying out XRD structural refinement of materials.The Rietveld method was used to refine the structural features of GTO.The high-resolution crystal XRD diffraction patterns of GTO with different concentration gradients were collected.Then,the relevant parameters of the crystal structure,such as lattice sites,ionic spacing,etc,were obtained by refinement with Full Prof software.The change of related cell parameters with the change of doping concentration was analyzed,and the schematic diagram of crystal structure was also made based on the results of refinement.Finally the effect of GTO crystal structure on the luminescence of Ln³⁺ions was analyzed through the above refined results.（3）We discussed possible up-conversion energy transfer mechanisms of GTO:x%Yb³⁺/1%Er³⁺（X=0-20）,and the application value in the field of temperature sensing were evaluated as well.（1）The power dependence and fluorescence kinetics of UCL has revealed that the mechanism two-phonon involved energy transfer processes should be the main contributions to the upconverted emissions.（2）We measured up-conversion spectra of phosphors in the range of 323K-523K,and the performance of optical temperature sensing was evaluated based on FIR technique.The results indicate that the maximum of absolute sensitivity was obtained to be 7.3×10^-3 K^-1 at 501 K,while the relative sensitivity was estimated to be 1013/T²,which achieves 9.7×10^-3 K^-1 at the starting temperature（323 K）of the present experimental measurement.The temperature resolution and repeatability were evaluated as well.The above results indicate such a material is promising in the application of optical temperature measurement.（4）A series of Tb³⁺,Dy³⁺,Eu³⁺mono-doped and Tb³⁺/Dy³⁺/Eu³⁺co-doped GTO luminescent materials were synthesized by hydrothermal method.The samples were characterized by XRD,excitation spectra,emission spectra and CIE coordinates.GTO:x%Dy³⁺（x=1.0-10）showed great yellow emission at 350 nm,with the main emission peak at 575 nm and the strongest yellow emission at concentration of 2.5%with color coordinates of（0.39,0.43）.GTO:x%Eu³⁺（x=0.5-10）exhibits good red emission at393 nm,with the main emission peak located at 614 nm,and the strongest red emission occurs at 7.5%Eu³⁺concentration.In addition,its actual luminous color is consistent with its color coordinates（0.62,0.38）.GTO:x%Tb³⁺（x=0.5-10）shows color change from blue violet light to green light with the increase of doping concentration.The color change of phosphor may be caused by the cross relaxation of Tb³⁺.When the concentration of doped Tb³⁺is 0.5%,the color coordinate of the sample is（0.33,0.35）,which is very close to color coordinate of（0.33,0.33）for white light illumination.Futhermore,the color rendering index of GTO:0.5%Tb³⁺is calculated to be as high as 85.69,which has a good prospect for lighting applications.By adjusting the doping concentration of the three ions for co-doping,a tunable luminescence color is achieved,and a warm white luminescence is obtained while reducing the associated color temperature.The luminescent materials obtained in this thesis exhibit excellent luminescence property and temperature sensing properties.and offers broad application prospects in the fields of solid-state lighting,multi-color luminescent elements and temperature sensing.The results of the experiment also provide some guidelines for the composition design and luminescence performance of rare earth ion-doped tellurite substrate materials...