Exploration Of Several Oxysalt Nonlinear Optical Crystals

Nonlinear optical crystals are a kind of important core crystal materials in laser frequency conversion technology,and have wide application value in optical communication,military,medical,aerospace and other high-tech fields.With the rapid development of laser technology,more requirements are put forward for nonlinear optical crystals.Therefore,the exploration of nonlinear optical crystals with excellent properties has become a research hotspot.In this paper,several oxysalt nonlinear optical crystals are explored.The main research contents and achievements are as follows:1.In the iodate system,two contained gallium iodate compounds,Ga（IO₃）₃ and Na Ga I₃O₉F,were synthesized and characterized by introducing alkali metal cations without d-d/f-f electron transitions,main group metal Ga³⁺cations and F^-anions with high electronegativity.The Ga（IO₃）₃ compound crystallized in the chiral space group P6₃.The crystal structure was formed by linking the Ga O₆^9-polyhedron with six IO₃^-units sharing O atoms to form the[Ga（IO₃）₆]^3-group,and further linking O atoms to form the 3D frame structure.Ga（IO₃）₃ exhibited a large band gap（3.94 e V）,good thermal stability（450℃）.The powder SHG effect was 13×KDP,and the phase matching could be achieved.The experimental and theoretical calculation results showped that Ga（IO₃）₃ is a potential infrared nonlinear optical crystal material.Na Ga I₃O₉F crystallized in the centrosymmetric P2₁/c space group,and two IO₃^-and IO₃F^2-anionic iodate groups appear simultaneously in the crystal structure for the first time.Na Ga I₃O₉F presented a 2D layered structure and was composed of_∞[Ga₂（IO₃）₄（IO₃F）₂]^2-polyanionic groups.Na Ga I₃O₉F exhibited a wide band gap of4.27 e V,good thermal stability up to 400℃,and large birefringence(Δn_exp=～0.203,Δn_cal=0.197@1064 nm).2.In tellurate system,two tellurate compounds with centrosymmetric Rb[Te₂O₄（OH）₅]and non-centrosymmetric K₂[Te₃O₈（OH）₄]were synthesized by introducing alkali metal cations without d-d/f-f electron transitions.They were crystallized in monoclinic space group P2₁/c and orthogonal space group Fdd2,respectively.Two tellurate compound structures contained two types of Te（VI）O₆^6-polyhedra:the terminal Te（1）O₆^6-and bridging Te（2）O₆^6-units.The two anionic units were connected by sharing corners and edges to form a 0D cluster(Te₄O₁₈)^12-polyanionic group and 1D chain_∞(Te₃O₁₂)^6-polyanionic group.The_∞(Te₃O₁₂)^6-polyanionic group was formed by a 0D cluster(Te₄O₁₈)^12-group further connecting the terminal Te（1）O₆^6-group and extending indefinitely.Both compounds exhibited wide optical band gaps of 4.15 e V and 4.05 e V,and moderate birefringenceΔn_exp=0.05 andΔn_exp=0.045.Under 1064 nm laser irradiation,the compound K₂[Te₃O₈（OH）₄]showed moderate power SHG effect,about 0.6×KDP,and could achieve the phase matching.3.Inπ-conjugated cyanourate（H_xC₃N₃O₃）^（3-x）-（x=0-3）system,three new hydrated isocyanurate compounds Li₂Zn₂（H₂C₃N₃O₃）₂（HC₃N₃O₃）（OH）₂·2H₂O（LZHCY）,Ba Zn₂（H₂C₃N₃O₃）₂（HC₃N₃O₃）（OH）₂·2H₂O（BZHCY）and Zn（H₂C₃N₃O₃）₂·3H₂O（ZHCY）were synthesized by introducing alkali metal/alkali earth metal and d¹⁰ transition metal Zn²⁺cation.LZHCY and BZHCY were isomorphic compounds,in which the isocyanurate anionic groups were connected by hydrogen bonds to form crown-type cluster anionic groups[（H₂C₃N₃O₃）₄（HC₃N₃O₃）₆]^16-（A^I）and[（H₂C₃N₃O₃）₄（HC₃N₃O₃）₄]^12-(A^II).LZHCY displayed a wide band gap of E_g=5.21 e V and a large birefringenceΔn_cal=0.174@1064 nm.In the ZHCY structure,the isocyanurate anionic groups exhibited a band structure with a band gap of E_g=5.24 e V and a birefringence ofΔn_cal=0.283@800 nm.