Synthesis,Structure And Properties Of Infrared Optical Chalcogenides With MQ₄(M=Zn,Cd,In,Ga,Al;Q=S,Se) Tetrahedra

With the development of semiconductor technology and laser technology in recent years,various new requests have been put forward for nonlinear optical materials.As a critical component of Frequency down-conversion solid-state lasers,infrared nonlinear optical crystals can realize laser frequency conversion through phase matching technology and output tunable medium far-infrared laser light,which has widely applications in information,energy,medical,industrial manufacturing,etc.Infrared nonlinear optical crystals such as AgGaS₂,CdS,and Zn Ge P,which are currently used in broadband infrared optical parametric oscillators.However,due to the low laser damage thresholds and crystal defects emerged during crystal growth,these materials can?t fully meet the growing demand for infrared nonlinear optical materials.Therefore,besides improving the quality of present infrared nonlinear optical crystals,the study of the relation between structures,compositions and properties of infrared nonlinear optical materials as well as exploratory syntheses of new materials has been a hot and important topic.As the two important atmospheric windows of 3-5?m and 8-14?m are in the mid-infrared range,the current exploration of infrared nonlinear optical crystals generally requires high transmission in the two ranges.Previous studies show that the MQ₄(M=Zn,Cd,In,Ga,Al)tetrahedral motif usually produces large second harmonic generation(SHG)response and can be used as an efficient structural unit for the design of infrared nonlinear optical materials.In this dissertation,seven novel infrared optical materials containing MQ₄ tetrahedral units have been prepared by high-temperature flux method,including Sr₅ZnAl₆S₁₅,Na₃Zn M^?Q₄(M=In,Ga;Q=S,Se),Ba₄F₄Zn Ga₂S₆and Ba₄F₃Ga S₄.Their structure and properties were studied by experimental and theoretical methods.(1)Sr₅ZnAl₆S₁₅.A quaternary chalcogenide with a non-centrosymmetric structure-Sr₅ZnAl₆S₁₅ was successfully synthesized by a conventional high-temperature flux reaction.The compound crystallizes in the orthorhombic Ama2(No.40)space group and its structural framework is formed by T2-supertetrahedron through an S-sharing chain and a vertex-sharing[Al₂S₇]chain formed by Al S₄ tetrahedron,and those two connected by a layer of S.This compound has a large band gap(3.16 e V,calculated)and excellent chemical stability.The band structure shows that Sr₅ZnAl₆S₁₅ is a direct bandgap compound.The SHG response of Sr₅ZnAl₆S₁₅ is about 0.26 times of Ag Ga S₂.The SHG-density shows that the SHG response of the compound mainly comes from the[Zn S₄]group and its birefringence is about 0.026,which can be used as a promising material for infrared frequency conversion.(2)Na₃Zn M^?Q₄(M=In,Ga;Q=S,Se).A suite of central-symmetric chalcogenides,Na₃Zn M^?Q₄(M=In,Ga;Q=S,Se),were successfully synthesized through element-substitution strategy by a high-temperature flux method.The compounds are crystallized in the tetragonal I4₁/acd space group.The structure consists of wavy chains linked by apex-sharing(Zn/M^?)₄Q₁₀ T2-supertetrahedra and charge-balanced Na.Interestingly,the connection of the Na S₆ motifs includes both vertex-sharing,edge-sharing and co-planar connections,which is different from other quaternary chalcogenides.In addition,there is a torsion angle of 24.613°between two nonadjacent supertetrahedra along the c-axis.The Na₃Zn M^?Q₄(M=In,Ga;Q=S,Se)compounds have a wide range of light transmission in the infrared range and photoluminescence effects,indicating potential applications in photoluminescence.(3)Ba₄F₃Ga S₄ and Ba₄F₄Zn Ga₂S₆.By inducing the halogens into chalcogenides to improve the bandgap and laser damage threshold,two new fluorine-containing chalcogenides with large bandgaps,Ba₄F₃Ga S₄ and Ba₄F₄Zn Ga₂S₆,were synthesized by a high-temperature flux method.The Ba₄F₄Zn Ga₂S₆ crystal crystallizes in the monoclinic P2₁/c space group,and its structure is a typical two-dimensional layered structure,whereas Van der Waals force serves as the main force between the layers.Ba₄F₃Ga S₄ crystal crystallizes in the tetragonal I4₁/a space group show a novel symmetrical porous structure,which is constructed by an eight-coordinated Ba connected with five F and three S.The performance characterizations of these two compounds confirm the large band gaps of 3.35 e V in Ba₄F₃Ga S₄ and 3.61 e V in Ba₄F₄Zn Ga₂S₆.And both of them show good transmittance in the infrared range.In order to understand the relationship between structure and properties,the band structure calculation and the density of states are performed using the first principles calculation.In addition,the calculated birefringence of Ba₄F₃Ga S₄ is0.047@1064nm.