Growth And Magneto-Optical Properties Of Sesquioxide TbYO₃ Crystal

With the rapid development of high-power solid-state lasers and optical communication technology,the demand for optical isolators in the visible near-infrared region in industrial production and scientific research is constantly increasing.However,traditional terbium gallium garnet（TGG）crystal,due to its small Verdet constant,not only require a medium length greater than 20 mm in industrial applications,but also a strong magnetic field,which cannot meet future high-power requirements in industrial applications.Developing a high-performance magneto-optical crystal can minimize length or magnetic field strength when constructing isolators.Tb₂O₃ is the material with the highest Verdet constant known,but its high melting point and complex phase transition matrix make it difficult to grow high-quality single crystals.In this paper,the doping of yttrium oxide in terbium oxide was studied.Large size(Tb_xY_1-x)₂O₃ magneto-optical crystals（x=0.3,0.5,0.7,1.0）were grown using laser floating zone growth technology at different doping concentrations.The optical and thermal properties of the grown crystals were characterized,and the magneto optical properties were measured.The main contents are as follows:The(Tb_xY_1-x)₂O₃ ceramic rods were prepared by cold isostatic pressing and high temperature sintering.Large-size(Tb_xY_1-x)₂O₃ crystals were grown by laser floating zone growth technology.The effects of different doping concentration ratios on the growth of(Tb_xY_1-x)₂O₃ crystals were explored.Finally,when the ratio of Tb:Y was1:1,a large-sized TbYO₃ transparent single crystal without obvious cracks was grown.The valence state of Tb element in the crystal is controlled by annealing in reducing atmosphere,and the TbYO₃ crystal whose main valence state of Tb element is Tb³⁺is obtained.After cutting and polishing the grown crystal,the composition and structure of the crystal were characterized by X-ray diffraction,rocking curve test,Raman scattering test,X-ray photoelectron spectroscopy,SEM,inductively coupled plasma emission spectroscopy（ICP-OES）and crystal structure analysis.The transmission spectrum and absorption spectrum of the crystal at the wavelength of 350-1750 nm were measured at room temperature,and the absorption coefficient of the crystal was calculated.The thermal conductivity of the crystal was calculated by measuring its thermal diffusivity,specific heat and density.The thermal properties of the crystal were determined by testing the thermal expansion coefficient and the laser induced damage threshold of the crystal.The extinction ratio and Faraday rotation angle of TbYO₃ crystal were measured by extinction method at different wavelengths,and the Faraday rotation angle of a commercial TGG single crystal was measured and compared with TbYO₃ crystal.The Verdet constants of TbYO₃ and TGG crystals at different wavelengths were calculated and compared,and the magneto-optical merit of TbYO₃ crystals at different wavelengths were calculated.The factors affecting the Verdet constant of the TbYO₃material were studied,and the results showed that the grown crystals had large Verdet constants and good magneto-optical properties.The large Verdet constants of TbYO₃crystal,combined with its excellent optical and thermal properties,make it a promising magneto optical candidate material.