Design, Synthesis And Characterization Of Mixed Alkali/Alkaline Earth Metal Borate NLO Material

Non-linear optical crystals are an essential part of solid-state lasers and are widely used in laser technology,optical communication,optical data storage,and optical signal processing.Utilizing the properties of nonlinear optical crystals,frequency conversion of various lasers can be achieved,which is a fundamental way to open up new laser light sources.Analysis and understanding of the relationship between structure and performance will guide the synthesis of new nonlinear optical crystal materials.This thesis aims to design and synthesize new UV/Deep UV optical crystal materials.A series of compounds have been synthesized by hydrothermal method and high temperature melt method.The main design strategy is:(1)Select two functional primitives,such as BO₃ and CO₃ with planar?conjugate,mix them into a system and arrange them in a coplanar arrangement.This structure makes the compound advantageous for obtaining a large birefringence.(2)Select alkali metals and alkaline earth metals without d-d or f-f electron transitions to widen the band gap of the borate.(3)The addition of the most electronegative charged F ions can effectively widen the transparent window of the material and is more suitable for ultraviolet applications.The main contents are as follows:1.A new strontium hydroxyborate Sr₅[BO₂(OH)]₃(OH)₃F was synthesized by hydrothermal method for the first time.Crystals are in the monoclinic space group P2₁/m.The basic building unit of this structure is[BO₂(OH)]^2-unit.Comparison of the structure of other strontium hydroxyborate shows that it is the first strontium hydroxyborate fluoride compound containing an isolated B-O group.The calculated band gap is about 4.94eV.First-principles calculations show that it has a moderate birefringence(0.067@1064nm).2.Using high temperature melt method,boron carbonate Sr₅(CO₃)₂(BO₃)was synthesized in an open system.With isolated BO₃ and CO₃ anion groups,Sr₃(BO₃)₂ layers and BaCO₂ layers are alternately stacked along the b direction.The structure analysis of anhydrous boron carbonate shows that the symbiotic layer structure is favorable for the synthesis of Sr₅(CO₃)₂(BO₃).The calculated band gap is 4.13eV.First-principles calculations show that the optical properties of Sr₅(CO₃)₂(BO₃)mainly come from the contributions of C-O groups and Sr-O groups.3.An alkali metal halide borate Li₃KB₉O₁₅F was synthesized by the high temperature melt method.It belongs to the R3c space group and is an asymmetric structure.It presents a three-dimensional network structure in space,consisting of a polyhedron and a three-dimensional frame composed of LiO₃F and KO₆F.It has a complex three-dimensional[B₉O₁₅]_?network structure.B₉O₁₉9 is composed of three B₃O₇ groups juxtaposed.Infrared spectrum test results verified the existence of BO₃ and BO₄ groups in the structure of the compound Li₃KB₉O₁₅F;UV-visible-near diffuse reflection test results showed that the above compounds have a lower cut-off edge,below 200nm.This shows that FBB formed by connecting alkali metal ions,F ions and B-O is an effective strategy for designing new required ultraviolet/deep ultraviolet photomaterials;electronic structure calculations indicate that this compound is a direct band gap compound.