Design And Characterization Of New Chalcogenides Infrared Nonliinear Optical Materials

The performance of infrared crystal materials has been put forward more and more high requirements with the development of science and technology as well as the popularization of the application of infrared crystal materials.Meanwhile,Mid-infrared laser plays an important role in civilian and military applications,and it is necessary to use infrared nonlinear optical crystal materials to convert the frequency of laser light source.The commonly used infrared nonlinear optical crystal materials,such as AgGaQ₂（Q=S,Se） and ZnGeP₂,have a strong second harmonic generation response and a wide transmittance in the infrared region,but there are a number of problems in those materials.For example,Ag Ga Se₂can not achieve the phase matching at 1μm and AgGaQ₂（Q=S,Se） have a low laser damage threshold as well as ZnGeP₂ has two-photon absorption at 1μm.All of those cases severely impeded the use of these materials.Therefore,researchers around the world attach great importance to exploring new infrared nonlinear optical materials with excellent properties.The main content of this thesis is to look for variety study systems and synthesize s series of compounds with noncentrosymmetric structure through high temperature solid state reaction based on the design of new chalcogenides infrared nonlinear optical materials as the goal.The structures of these compounds were analyzed and compared,and their properties were tested and their applications in infrared nonlinear field were evaluated.At the same time,it is hoped that the research work of this paper can provide valuable references for the subsequent design and synthesis of new infrared nonlinear optical crystal materials.1.Synthesis and characterization of a new infrared nonlinear optical crystal materials SnZnSnQ₄（Q=S,Se）.Two new infrared nonlinear optical crystal materials Sr ZnSnS₄ and SrZnSnSe₄ were found in family of A^Ⅱ-M^Ⅱ-X^Ⅳ-Q₄（A=Ba,Sr;M^Ⅱ=Zn,Cd,Hg;X^Ⅳ=Si,Ge,Sn;Q=S,Se）.They all belong to noncentrosymmetric structure Fdd2 space group of orthorhombic system.The structure was composed of ZnS₄（ZnSe₄） and SnS₄（SnSe₄）tetrahedrons,which connect to each other to form a two-dimensional infinite[Zn-Sn-S]（[Zn-Sn-Se]）layer structure,and Sr atoms are orderly arranged in the layers.In terms of optical properties,the band gaps of SrZnSnS₄ are 3.37 eV and 2.83 eV through upper tangent method and baseline tangent method,respectively.The band gap of Sr Zn Sn Se₄is 2.04 e V.The second harmonic generation effect of Sr Zn Sn S₄is approximately equal to that of LiGaS₂(d₃₁=5.8pm/V)and it can achieve the phase matching behavior.The theoretical calculation shows that the SHG effect of SrZnSnSe₄is equivalent to that of AgGaSe₂(d₃₆=33 pm/V).In addition,the structures,band gaps and nonlinear optical effects of other compounds in family of A^Ⅱ-M^Ⅱ-X^Ⅳ-Q₄（A=Ba,Sr;M^Ⅱ=Zn,Cd,Hg;X^Ⅳ=Si,Ge,Sn;Q=S,Se） were compared.2.Synthesis and characterization of a new infrared nonlinear optical crystal materials Cu₂SrSiS₄.A new infrared nonlinear optical crystal material Cu₂SrSiS₄ was found in family of A₂^I-M^II-X^IV-Q₄(A^I=Li,Na,K,Cu,Ag;M^II=Ba,Sr;X^IV=Si,Ge,Sn;Q=S,Se)and it crystallized in the noncentrosymmetric structure P3₁2₁ space group of trigonal system.The structure is characterized by the fact that each SiS₄ tetrahedron connects to eight Cu S₄ tetrahedrons by sharing S atoms,while each CuS₄ tetrahedron links with a Cu S₄ tetrahedron and a SiS₄ tetrahedron by sharing S atoms.Finally,Cu S₄ and SiS₄ tetrahedrons are connected to form a three-dimensional frame structure,and Sr atoms are distributed in the holes of the frame structure.As regard to the nonlinear optical properties,the experimental band gap of Cu₂SrSiS₄ is 2.51 eV.Besides,we also compared and analyzed the band gaps of other compounds in this family and summarized some rules.