Fabrication And Property Optimization Of Yb:YAG Nano-powders Synthesized By Wet-chemical Method And Transparent Ceramics

Solid-state lasers have broad application prospects in industry,military,medical science and other fields.The gain medium composed of matrix materials and active ions is key component of solid-state lasers.The yttrium aluminum garnet(Y₃Al₅O₁₂,YAG)matrix show high thermal conductivity,uniform doping of active ions and simple preparation of large-size and composite samples.These characteristics make them a promising candidate for gain matrix materials.Yb³⁺exhibits simple energy level structure,long fluorescence lifetime,broad absorption and emission band,high gain,and high doping concentration in YAG matrix.Therefore,Yb:YAG ceramic is a gain medium with excellent comprehensive performance for high-power solid-state lasers.High-quality powders are critical to the preparation of high-quality laser ceramics.Compared to the most commonly used solid?state reaction method,wet-chemical method mix elements at atomic scale,and the obtained nano-powders show high purity,good dispersibility,and high sintering activity.This makes the wet-chemical method very advantageous in the preparation of Yb:YAG ceramics with large size and high optical quality.Based on the above viewpoints,5at.%Yb:YAG nano-powders were prepared by co-precipitation method.5at.%Yb:YAG ceramics were fabricated by vacuum sintering and vacuum pre-sintering with HIP post-treatment.The synthesis of powders and sintering of ceramics were studied,and 5at.%Yb:YAG ceramics with high optical quality were fabricated.The main contents are as follows:1)5at.%Yb:YAG nano-powders were prepared by the co-precipitation method using pure water and alcohol-water mixture as the solvents.The composition,morphology and agglomeration degree of the powders were studied.Compared to the powder with pure water solvent,the powder with alcohol-water solvent exhibits the same composition,smaller average crystallite size and lower agglomeration degree.2)The influence of calcination temperature on the properties of 5at.%Yb:YAG powder was studied.Using the powders calcined at different temperatures as raw materials,ceramics were prepared by vacuum sintering.Powders calcined at 1100-1300^oC show pure YAG phase.Although high calcination temperature reduces the sintering activity and improves the agglomeration degree of powders,it increases the relative density of green bodies.The ceramic with the powder calcined at 1250? shows the highest in-line transmittance.Taking the above factors into consideration,the powder calcined at 1250? for 4 h will be used for the subsequent fabrication of ceramics.3)Based on the previous work,the vacuum sintering temperature and holding time were optimized to improve the properties of 5at.%Yb:YAG ceramics.Spectroscopic properties of the ceramic with the highest in-line transmittance were calculated.The ceramic sintered at 1800? for 50 h shows the highest in-line transmittance of 78.6%at 1100nm and 76.7%at 400nm(2.2mm thickness).The full width at half maximum of emission peak at 1031nm of the gain cross section is wide,which is beneficial for the output of wide band tuning and ultrashort pulse laser.4)Based on the previous work,5at.%Yb:YAG ceramics were prepared by short-time vacuum pre-sintering and HIP post-treatment.The influence of pre-sintering temperatures on the properties of ceramics was studied.The in-line transmittance of the ceramic pre-sintered with HIP post-treatment increases with the increase of pre-sintering temperature.The ceramic pre-sintered at 1800? with HIP post-treatment shows the highest in-line transmittance of 72.7%at 1100nm(2.2mm thick).5)Based on the previous work,5at.%Yb:YAG ceramics were prepared by vacuum sintering and HIP post-treatment using the nano-powders without sintering additives and with Mg O as starting materials.The influence of Mg O on the optical properties of ceramics was studied.The results show that Mg O helps to improve the in-line transmittances of ceramics.The ceramic with Mg O sintered at 1825? with HIP post-treatment shows the highest in-line transmittance of 83.3%at 1100nm(1.8mm thick).The XEL pattern shows the presence of Cr³⁺in the ceramic.Mg O promotes the transformation of Cr³⁺to Cr⁴⁺,which causes the annealed ceramics with Mg O to turn orange and exhibit abnormal absorption peaks.