Fabrication And Performance Of Holmium Based Magneto-optical Transparent Ceramics

A magneto-optical transparent ceramic is a new type of magneto-optical medium material that has appeared in recent years.It has the advantages of high Verdet constant,high thermal conductivity,high laser damage threshold,and large size.It is the most ideal material for faraday isolators in high-power lasers.one.Due to the higher inherent concentration of rare earth cations,the lanthanide sesquioxide has a larger field constant than the garnet structure studied in previous years.This dissertation project carried out the preparation and performance research of holmium oxide-based magneto-optical transparent ceramics.Synthesis of nitrate type rare earth layered compound（Ln₂（OH）₅NO₃·n H₂O）LRH precursor by low temperature precipitation method,which is difficult to be used directly to produce oxide powder with high sintering activity,However,after in-situ exchange of sulfate and nitrate ions,the corresponding sulfate-type LRHs can be obtained,get high sintering activity Ho₂O₃nano powder is suitable for the sintering of ceramics.The influence of the calcination temperature of Ho₂O₃ powder on the optical quality of the sintered body was investigated in detail.The effects of HoOF synthesized by self-reaction as an additive on the magneto-optical properties and microstructures of Ho₂O₃ ceramics were focused on,and the effect of Dy³⁺doping concentration on the(Dy_xHo_1-x)₂O₃ verdet constant was investigated.The main research results obtained from this dissertation work are summarized as follows:（1）Under the condition of low temperature and humidity,the rare earth layered compound obtained by nitrate ion exchange between sulfate ion exchange layers is used as the precipitation precursor,and the round oxide powder with high sintering activity after calcination,through investigation,the best calcination temperature is 1050℃.The linear transmittance of Ho₂O₃ ceramic at 1064 nm after vacuum sintering reached 73%,which is close to its theoretical transmittance of 90%;the magneto-optical performance is 1.3 times that of the commercially available TGG,showing the good application potential of Ho₂O₃magneto-optical transparent ceramics in high-power laser systems.（2）Using F^-as an additive,that is,a direct chemical reaction of holmium-based LRH and NH₄F in a weak acid generates a homogeneous mixture of Ho₂（OH）₅NO₃and Ho₂（OH）₂F,which is calcined to obtain Ho₂O₃ powder containing secondary phase HoOF.The results show that:at the F^-/Ho³⁺molar ratio（R=0.01）,a high optical quality transparent Ho₂O₃ceramic with a transmittance of～72.0%at 1550 nm was prepared by vacuum sintering at1850℃.The measured Verdet constants at 633,1064 and 1550 nm were-181,-46 and-22rad/（T.m）（1.3 times of terbium-gadolinium garnet TGG）.（3）A series of(Dy_xHo_1-x)₂O₃ optical ceramics based on holmium oxide were successfully prepared by vacuum sintering,where（x=0.01-1）,its online transmittance at 1500 nm wavelength 70～77%.The effect of Dy³⁺doped holmium oxide on optical and magnetic properties was studied in detail.The results show that the Verdet constant of magneto-optical(Dy_xHo_1-x)₂O₃increases with the increase of Dy³⁺content,When x=1.0,the verdet value at 635nm is-356 rad/（T.m）,which is about 2.6 times that of the commercially available TGG.Especially at 1900-2200 nm,there is no absorption and the transmittance reaches（T=71.5%）,so it can be used in Faraday isolation devices and Faraday rotators,as well as Tm³⁺and Ho³⁺ lasers.