Synthesis And Infrared Nonlinear Optics Property Investigation Of Quaternary Selenides

In laser frequency conversion technology,nonlinear optical(NLO)materials are an important component,and they play an important role in laser science and laser technology applications.With the development of laser technology in the military and business,people have higher requirements for nonlinear optical materials.Among many nonlinear optical materials,Ge Q₄ tetrahedrons and Sb Q₃ pyramids(Q=S,Se)are generally used as the basic units of the structure,which exist alone in zero-dimensional compounds or pass through shared vertices,shared edges and shared surfaces in multi-dimensional compounds long chain,plane and body.However,there are also a small number of compounds that exist alone to form a new dimer basic structural unit by combining two basic structural units.The existence of non-centrosymmetric basic elements in the structure is of great significance to form a non-centrosymmetric structure and generate a strong second harmonic generation(SHG)response.These new symmetrical basic unit composed of two basic units provide the design of non-centrosymmetric structures new ideas.On this basis,the compound Ba₂Sn Ge Se₅ was synthesized by the high-temperature solid-phase method and crystallized into an orthorhombic Pnma space group with a centrosymmetric zero-dimensional structure.There is a basic structural unit Ge Sn Se₅ dimer,the element Sn is+2 valence,and the experimental band gap 1.63e V has high thermal stability.Compounds Rb₄Ge₄Se₁₂ and Cs₄Ge₄Se₁₂ have[Ge₂Se₄(?-Se₂)]^4-dimers,in which Se-Se bonds have an important contribution to the second harmonic generation.Compound Ba₂Sn Se₅and compound Ba₄Sn₂Se₁₀ have interesting Se₃^2-basic units.Contact the aforementioned Se-Se bond to the second harmonic generation,so try to add Se₃^2-basic units to the structure of infrared nonlinear optical(IR NLO)crystal.We finally synthesized the compound Ba₄Ge Sb₂Se₁₁ crystallized into an orthorhombic Cmc2₁space group,a non-centrosymmetric zero-dimensional structure,consisting of basic structural units[Ge Sb Se₅]^3-,[Sb Se₃]^3-,and[Se₃]^2-.Compound Ba₄Ge Sb₂Se₁₁ has an experimental band gap of 1.35e V,which has high thermal stability,but its synthesis temperature is much higher than its decomposition temperature,which may deteriorate the quality of the final product crystal,which leads to its nonlinear optical performance test only the maximum particle size detection to the frequency-doubled signal,and only 0.2 times of Ag Ga S₂.As a cation with d¹⁰ electron energy level,Cd²⁺easily forms a distorted non-centrosymmetric basic unit with Q^2-(Q=S,Se)due to the second-order Jahn-Teller effect(SOJT).Therefore,in the process of trying to synthesize compounds containing Cd elements,the final synthesis compound Ba Cd Ge Se₄ crystallizes into an orthorhombic Fdd2 space group,a non-centrosymmetric two-dimensional layered structure,and has high thermal stability.The experimental band gap is 1.67e V,Non-phase matching,the maximum frequency doubling intensity is achieved at a sample particle size of 45-74?m,which is 0.5 times that of AgGaS₂.