Effect Of Adjusting Gd-site On Optical Properties Of Vacuum Sintered Gadolinium Zirconate Transparent Ceramics

As a functional material,transparent ceramics not only possess the general optical properties of traditional transparent materials,but also exhibit high stability,high strength and other characteristics that enable them to serve in special environments.The current research work focuses on the improvement of ceramic properties to promote their practical applications.Cubic structure Gd₂Zr₂O₇ can be prepared into transparent ceramics,and its Gd³⁺can buffer the aggregation of fluorescent ions and improve its fluorescence properties.In the past,its preparation process parameters were systematically explored,and their doped fluorescence properties were also preliminarily studied.In order to further improve the optical properties of Gd₂Zr₂O₇ transparent ceramics,the non-stoichiometric design concept and high-entropy design concept were introduced to transform the crystal energy band structure.The specific research work and results are as follows:（1）Firstly,the defective fluorite structure Gd_2+XZr₂O_7+3X/2 powder with grain size of 40nm was prepared by the combustion method.The shift of the diffraction peak was due to the distortion of the crystal caused by non-stoichiometric defects.The diffraction peaks of the ceramics are very sharp,and the characteristic peaks of pyrochlore gradually weaken and disappear with the increase of|X|,which indicates that the degree of order of the ceramics gradually decreases.The characteristic peaks of pyrochlore can be used to judge whether there is pyrochlore structure.Non-stoichiometric designs alter the structure and properties of ceramics.When the defects accelerate grain boundary migration and promote sintering,ceramics will exhibit large grains,few pores and high transmittance;while these defects inhibit atomic diffusion,which will result in residual pores that are detrimental to optical performance.With the increase of Gd content,the short-wave absorption limit of ceramics is blue-shifted,and the optical band gap becomes wider.（2）Subsequently,the fluorescence properties of Nd³⁺or Sm³⁺doped non-stoichiometric gadolinium zirconate transparent ceramics were studied.Powders and ceramics both exhibit single-phase structure,indicating that Nd³⁺or Sm³⁺is incorporated into the host lattice.Few non-stoichiometric defects（|X|≤0.3）can promote grain growth and eliminate pores,which will optimize the in-transmittance of ceramics;while excessive defects cause residual pores and degrade optical transparency.Defects are conducive to energy transfer and optimize fluorescence performance,but the increase of Nd³⁺concentration will produce cross relaxation and degrade fluorescence performance.The fluorescence intensity of Gd₁Nd_0.2Zr₂O_5.8ceramics is the highest.Non-stoichiometric defects have little effect on the fluorescence lifetime of Nd³⁺,and there is no concentration quenching.The optimal excitation and emission wavelength of Sm³⁺is 404 nm and 615 nm.The fluorescence change of Gd_1.8-XSm _XZr₂O_7+3X/2ceramics is caused by defects and cross-relaxation,and the fluorescence performance of Gd₁Sm_0.2Zr₂O_5.8 ceramics is the best.The fluorescence intensity of Gd₁Sm_0.2Zr₂O_5.8 ceramics is the highest.The charge transition state transition formed by oxygen vacancy makes the excitation spectrum exhibit an excitation peak at 265 nm.（3）Finally,the high-entropy design concept was introduced to prepare high-entropy Gd₂Zr₂O₇ transparent ceramics.The phase structure and grain size of multi-component A₂Zr₂O₇ transparent ceramics are affected by A-site rare earth ions.When the average radius of A-site ions is small,the ceramics are composed of large-sized defective fluorite grains.With the increase of A-site ions,the grain size decreases and the structure more ordered.When there are rare earth elements with a large difference in radius at the A-site,the difference in element diffusion will lead to element segregation,and the ceramic is composed of multiphase small grains.The high entropy effect can refine the powder particles,improve the sintering driving force and reduce the sintering temperature.In the high-entropy design,the rare earth elements are uniformly distributed in the ceramic,and the sensitization of Yb³⁺optimizes the up-conversion luminescence performance of Er³⁺.Therefore,the incorporation of Sm³⁺will reduce its fluorescence intensity,the multi-element fluorescence synergy is complex and nonlinear.This concept provides a new solution for optimizing the fluorescent properties of ceramics.