| As one of the most important inventions in 21 century,laser has played an important role in national security,scientific research,medical care and daily life after continuous research and development for decades.Thanks to the small volume,high stability and simple structure,solid-state laser has become the focus of laser research,and lead the development of laser research.Laser materials mainly include crystals,ceramic,glass and fiberetc.The disordered crystals possess excellent thermal properties and spectral characters,integrates the advantages of crystals and glass,which become great pulse laser materials.Although mixed crystals perform long-range order in structure,the active ions will occupy different sites randomly to substitute other ions in the mixed crystals.Therefore,the lattice fields surrounding them are different.Different active ions have different fluorescence lines,which overlap with each other then the total fluorescence lines get broad,which called inhomogeneous broadening.Finally,mixed crystals with their wide fluorescence lines and excellent thermal properties,become suitable for pulsed laser materialsVanadate crystals especially YVO4 are kinds of excellent laser material.GdVO4 and LuVO4 are homolog of YVO4,and also have excellent laser properties.They all belong to tetragonal system,whose melting point are more or less 1800?.High quality LuGdVO4,YGdVO4M YLuVO4 are grown by Czochralski method,and lots of research had been done about these materials.Their spectra possess obvious inhomogeneous broadening and they have been demonstrated to be excellent pulse laser materials.Er3+ doped materials are widely investigated as laser media for emitting eye-safe laser radiation,which can be used in many important fields such as range finding,optical communication,remote sensing,and medical treatment.Those materials have small absorption cross-sections and narrow full width at half the maximum(FWHM)of the absorption band around 980 nm,which are not favorable to AlGaAs or InGaAs laser diode pumping.Er3+/Yb3+ co-doping can improve the pump absorption efficiency of materials.Because of a strong and broad absorption band around 980 nm,Yb3-can transfer energy to Er3+ as a sensitizer in materialsAlthough there have been many reports about vanadate crystal doping.There have been no relevant reports about Er,Yb:LuGdVO4.For the first time,large size Er,Yb:LuGdVO4 series crystals were grown by Czochralski.Previous studies on vanadate crystals have focused on the growth and optical properties of mixed crystal whilewe pay more attention to the growth of crystals and the structure of mixed crystal.In this thesis high quality LuGdVO4 and Er,Yb:LuGdVO4 were successfully grown and the component,crystal structure,thermal and optical properties of crystals have been characterized.The effects of the annealing process on the structure and properties of crystal and crystal phase transition caused by high temperature annealing process were all studied at the same time.The outline is shown as follows1.Study of crystal growth and defectsHigh quality LuGdVO4 and Er,Yb:LuGdVO4 mixed crystal were successfully grown by Czochralski method.One brief introduction about the Czochralski method and the growth equipment is shown.The problems were also discussed in the growth processes.The best growth parameters are explored by experiments and optimized by numerical simulation2.Components and structures of crystalThe components of LuGdVO4 and Er,Yb:LuGdVO4 mixed crystal were determined by X-ray fluorescence,and the segregation coefficient of all the elements were calculated.The mixed crystal structure was analyzed by X-ray diffraction,and the crystal belongs to tetragonal system.The effect of composition on crystal structure was studied.The atomic vibrations and bond energy of LuGdVO4 and Er,Yb:LuGdVO4 were calculated by Raman spectra and XPS.In addition,the element distribution of the crystal was characterized by synchrotron radiation X-ray fluorescence(SR-based XRF)3.Thermal and optical propertiesThe thermal properties of LuGdVO4 and Er,Yb:LuGdVO4 mixed crystal were studied by analyzing specific heat,thermal expansion coefficients and thermal diffusivity.The spectroscopic characterizations of Er,Yb:LuGdVO4 mixed crystal,including the polarized absorption spectra and fluorescence spectra were recorded at room temperature.Spectral parameters such as the intensity parameters(?2,?4 and ?6),oscillator strengths,radiative transition probability and radiative lifetime of Er3+ were calculated by Judd-Ofelt theory.All the results suggest that Er3+/Yb3+:Lu0.5Gd0.5VO4 crystals can be an excellent candidate laser material.4.Secondary annealingThe Er/Yb:Lu0.5Gd0.5VO4 crystal with cooling fast process has been grown by the Czochralski method in the oxygen-deprived conditions,then annealed at different annealing process condition.The Effects of different annealing process conditions on the structure,chemical states and local symmetry of Er,Yb:LuGdVO4 were studied by XRD,Raman,XPS and XANES in detail.The specific heat,thermal diffusion and polarization absorption spectra of samples obtained under different annealing conditions were studied.the element distributions of the samples were characterized by synchrotron radiation X-ray fluorescence(SR-based XRF).5.Study of crystal phase transitionEr,Yb:LuGdVO3 was obtained by annealing the Lu0.5Gd0.5VO4 crystal at 1500 0C under vacuum condition.The X-ray fluorescence analysis method was used to measure the concentrations of Lu and Gd elements in Lu0.5Gd0.5VO4.The XRD result indicated that Er,Yb:LuGdVO3 was the orthorhombic structure with space group Pbnm.The lattice constants are calculated as a = 0.530 nm,b = 0.559 nm and c = 0.760 nm.The Raman spectrum of Er,Yb:LuGdVO3 was investigated at room temperature.The chemical states and local symmetry of the Er,Yb:LuGdVO3 crystal have been determined by XPS and XANES.It was found that the presence of different chemical forms of V evolved with annealing treatment,and the VO6 unit in the Er,Yb:LuGdVO3 crystal was distorted octahedron.During the annealing process at high temperature under vacuum condition,Er,Yb:LuGdVO3 can be gradually translated to Er,Yb:LuGdVO3 with decreasing lattice oxygen in the crystal lattice. |
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