Preparation And Laser Properties Of Yb³⁺ Doped LuAG Transparent Ceramics

The progress of human society can not be separated from the development of new materials,and the development and application of new materials also promote the development of science and technology and the progress of human civilization as well.Since 1995,the world's first high-quality YAG transparent ceramic was developed,transparent ceramics have gone through more than 20years.Translucent or translucent ceramics such as sesquioxide,Garnet-type oxides,silicate systems etc.are widely used in transparent windows,inorganic scintillators,LED and solid-state laser excitation media.Compared with the YAG matrix,Yb³⁺ion doped lutetium aluminum garnet(Yb³⁺:Lu AG)has a large effective atomic number Z_eff,high emission cross section and can keep good thermal conductivity at high Yb-ions doping concentration.Therefore,Yb:Lu AG single crystals and ceramics are widely used as matrix materials for solid-state lasers.High optical quality crystals have always been the main choice for various laser materials.However,the high melting point of Lu AG single crystal has a high growth temperature,a limited size and easy introduction of reverse defects between Al³⁺and Lu³⁺,which has affected the application of single crystal materials to some extent.For some special cubic structured materials,the nowadays transparent ceramic technology is possible to realize large size,low cost and high power transparent ceramic laser output.Therefore,it is important to develop transparent Yb³⁺:Lu AG optical grade ceramics,to study optical properties and to design suitable laser structures.At the moment,there are two main technologies for preparing laser grade Yb³⁺:Lu AG transparent ceramics.One is the solid phase reaction vacuum sintering technology represented by World Lab.,and the other is the nanocrystalline vacuum sintering technology represented by the Conoshima Chemical Co.Ltd.There are many research teams engaged in solid state reaction sintering at home and abroad.The related research covers almost all materials systems,and many reports are made on the preparation and laser performance of transparent ceramics.However,nanocrystalline vacuum sintering technology has only a few units with core technology and few details of ceramic preparation were reported.In this paper,Yb³⁺:Lu AG is selected as the research object,and a nanocrystalline sintering technology in following pressure less H₂ atmosphere is proposed.The synthesis of Yb:Lu AG nanopowders,the sintering of transparent ceramics and the laser properties of Yb³⁺:Lu AG transparent ceramics are systematically investigated:?1?Lu AG pure phase nanocrystalline powders with uniform particle size distribution and good sintering activity were synthesized by reverse titration co-precipitation process.The research shows that the pH value of the initial precipitant is controlled between 8-8.2 and the end of precipitation pH is controlled at about 6.4;?2?In addition of the precipitation pH value,the calcination temperature of precursor has a great influence on the sintering activity of powders.TG-DSC analysis of precursor showed that the precursor,synthesized by reverse strike precipitation co-precipitation method,formed Lu AG phase at 1016 ?.When the calcination temperature ranged from 1100? to 1400?,the primary particle size of Lu AG nanopowders is in the range of 50-200 nm.When the powder calcination temperature increases to 1350? and above,the pre-sintered phenomenon of the calcined powder is not conducive to sintering densification.When the calcination temperature is set to 1300?,even though there is a small amount of"neck"between adjacent Lu AG particles,which does not affect the transparency of ceramic sinter processing;?3?Lu AG ceramics with better transparency can be obtained by sintering at1700 ? for 5 h in flowing hydrogen atmosphere.With the increase of sintering temperature,and a long holding time extending to 10 h,the transparecy of Lu AG ceramic,2.5 mm in thick,reached the overall rate of more than 80%in the visible band from 400 nm to 800 nm.We can draw a simple conclusion that the reverse drop coprecipitation and pressureless sintering in hydrogen is an effective method for the preparation of Lu AG transparent ceramics;?4?On the basis of process optimization,we propose a nanocrystalline pressureless hydrogen sintering?NC-PLSH?technique to successfully prepareing the laser grade 3at.%Yb³⁺:Lu AG ceramics between 1750-1800 ?/20h.The optical homogeneity analysis shows that the thickness of the 2.5mm ceramic sample is equivalent to that of the commercial YAG single crystal,which has the basis for developing high performance Yb³⁺:Lu AG ceramic laser;?5?Pumping by a single laser diode tube with 940nm wavelength,we successfully realized laser generation of the 0.91W laser output by suing the homemade 3at.%Yb³⁺:Lu AG transparent micro-chip ceramic.The laser output wavelength is around 1030 nm,and the optical to optical conversion efficiency is58%without any colling conditions;?6?Under the help of Physics Research Institute of Russian Academy of Sciences,we successfully realized a 206W continuous wave laser output,by using our home made 3at.%Yb³⁺:Lu AG transparent ceramic thin-disk?300nm in thickness?,where a multi-pass pumping of 12 channels with a 940nm laser diode was designed as a multi-puming optical system,and the maximum slope efficiency reached as high as 54%.?7?Based on Nanocrystalline hydrogen pressureless sintering technology and the optimized pure Lu AG and Yb³⁺:Lu AG transparent ceramics fabrication parameters,4at.%Tm³⁺:Lu AG and 7 at.%Yb³⁺,4at.%Tm³⁺-codoped Lu AG transparent ceramics with grain size was of about 2-5?m were successfully prepared.The linear transmittance of as polished ceramics in the visible light reached 81%?1mm in thickness?.High quality Tm³⁺:Lu AG transparent ceramic is one of the most efficient laser materials for the 2?m emission.It is expected to be used in the field of human eye safety laser and radar detection.This doctoral dissertation presents the nanocrystalline hydrogen pressure sintering technology,which can realize the preparation of laser grade Yb³⁺:Lu AG transparent ceramic,with fine grain crystallite of about 1-2?m,free of sintering aids.Our route pave up another way to fabricating laser grade Lu AG transparent ceramic after solid phase reaction vacuum sintering and nano-crystalline vacuum sintering technology.Through the study of the relationship between preparation,material structure,optical quality and laser performance of Yb³⁺:Lu AG transparent ceramic,it is expected to lay a foundation for the high efficiency laser output of domestic high-power Yb³⁺:Lu AG laser ceramics.