The Study Of New Infrared Nonlinear Optical Mateirals In Alkaline Metal Chalcogenides Systems

Infrared nonlinear optical crystal,as the core device of solid-state laser frequency conversion,can realize the transformation of laser frequency through phase matching technology,and output tunable mid-far-infrared laser source,which has been widely used in information,energy,medical treatment,industrial manufacturing and other fields.At present,only a few IR NLO materials have been used in commercialization,such as AgGaS₂,AgGaSe₂ and ZnGeP₂,However,their application ranges are seriously hindered by the inherent performance defects,such as their small band gaps lead to their low laser damage thresholds or serious two-photon absorption.Generally,wide bandgap（Eg）is corresponding to a high LDT,but inversely proportional to the large SHG coefficient(d_ij)in one material.Therefore,to explore new infrared nonlinear optical materials with balanced large SHG and high laser damage threshold properties has become a very important research direction.This thesis mainly in order to design a new type of chalcogenide infrared nonlinear materials as the goal,with alkali metal,d¹⁰ cations and antimony element as the research system,then synthesized compounds with solid-state reaction technique in fused silica tubes.Their optical performances were also investigated.Moreover,theoretical calculation was also used to analyze the structure-performance relationship.1.A promising IR nonlinear optical material Li₂ZnGeS₄ with high optical performances is synthesized.A promising infrared nonlinear optical（IR NLO）material,Li₂ZnGeS₄,was successfully synthesized in the typical quaternary diamond-like semiconductors（DLSs）system.This material exhibits the excellent performances including wide band gap（3.49 eV）,high laser-damage threshold（LDT,8×benchmark AgGaS₂）,and good NLO effect（0.7×AgGaS₂）with phase-matching behavior.Furthermore,based on the first principles calculation,theoretical results are in agreement with the experimental results.2.Investigation on two new antimony-based quaternary chalcogenides:Na₆CdSb₄S₁₀ and Na₃CdSbSe₄Two new quaternary chalcogenides,Na₆CdSb₄S₁₀ and Na₃CdSbSe₄,were successfully synthesized by the high-temperature solid-state reaction in vacuum-sealed silica tubes.Note that Na₆CdSb₄S₁₀ crystallizes in the C2/c space group,whereas Na₃CdSbSe₄ crystallizes in the P2₁/c space group.Seen from their structures,Na₆CdSb₄S₁₀ exhibits a three-dimensional（3D）framework structure composed by the interconnection of isolated[（Cd/Sb）₂Sb₂S₁₀]clusters and two different layers formed by the NaS_n（n=4,6）units,besides,the structure of Na₃CdSbSe₄ is composed of isolated_∞(Cd₃Sb₂Se₁₂)_n chains and 2D layers formed by the NaSe_n（n=5,6）units.Their optical performances（bandgap and Raman spectra）were also investigated.Moreover,theoretical calculation was also used to analyze the structure-performance relationship of Na₃CdSbSe₄.3.Na₆MQ₄（M=Zn,Cd,Q=S,Se）:Promising Infrared Nonlinear Optical MaterialsIn this paper,four new ternary chalcogenides were successfully synthesized by the high-temperature solid-state reaction for the first time.They are crystallized in the hexagonal P6₃mc space group,main structure is the three-dimensional network structure formed by the isolated ZnS₄ group connected with three Na（1）S₄tetrahedrons and three Na（2）S₅ pentahedrons through Shared sulfur atoms.Large optical band gap of 3.47 eV（Na₆ZnS₄）,1.79 eV（Na₆ZnSe₄）,2.92 eV（Na₆CdS₄）and1.85 eV（Na₆CdSe₄）,wide transparent region of 0.25-2μm,and with good NLO responses（0.3–1.1×AgGaS₂）with phase-matching behavior.All these performance studies indicate that Na₆MQ₄（M=Zn,Cd,Q=S,Se）is a promising candidate material for infrared NLO,which can be used in high-energy laser systems.