Exploration Of Selenite Nonlinear Optical Crystal Materials

Non-linear optical crystal is a key material for laser frequency conversion.The exploration of nonlinear optical materials with large nonlinear optical coefficient,moderate birefringence and good thermal stability has important application value and academic significance.In this thesis,we synthesized four kinds of non-centrosymmetric selenite crystal materials by the method of medium temperature and medium pressure hydrothermal,their structures and basic properties were systematically studied.(1)In the Pb-M-Se-O-Br system,two kinds of non-centrosymmetric compounds were obtained for Pb₂Ga F₂(Se O₃)₂Br and Pb₂Nb O₂(Se O₃)₂Br.They all belong to the polar space group P2₁,and the unit cell parameters are a=8.3926(6)(?),b=5.4095(3)(?),c=10.6751(8)(?),?=?=90°,?=111.049°,Z=2.The two compounds are isostructural with each other,and the three-dimensional frameworks are composed of1D(Pb₂Br)³⁺cationic chains and 2D[Ga₂F₄(Se O₃)₄]^6-/[Nb₂O₄(Se O₃)₄]^6-anionic chains.We have tested some basic physical and chemical properties of these two compounds.The powder frequency doubling responses of the two compounds are 4.5×KDP and1.4×KDP,respectively.The band gaps of the two compounds are 3.73 e V and 3.17 e V,respectively,and they have good thermal stability(>425?).Both of the two compounds can achieve I-type phase matching,which is advantageous for nonlinear optical applications.(2)In the Y-Se-O system,there were obtained two kinds of non-centrosymmetric compounds Y₃(Se O₃)₄F and Y(HSe O₃)(Se O₃)(H₂O)·(H₂O).Y₃(Se O₃)₄F belongs to the polar space group P6₃(No.173),and the unit cell parameters are a=10.0247(3)(?),b=10.0247(3)(?),c=7.1627(4)(?),?=?=90°,?=120°,Z=1.9998.The six-membered ring structure is composed of a YO₇F polyhedron distributed along the c-axis and(Se O₃)^2-by sharing O atoms.Y(HSe O₃)(Se O₃)(H₂O)·(H₂O)belongs to the polar space group P2₁2₁2₁.The polyhedrons of YO₈,Se O₃ and HSe O₃ are connected together by sharing corners and edges to form a two-dimensional layered structure.The powder frequency doubling effects of Y₃(Se O₃)₄F and Y(HSe O₃)(Se O₃)(H₂O)·(H₂O)are 0.6 and 0.5 times that of KDP(KH₂PO₄),respectively.In addition,Y₃(Se O₃)₄F has a wide band gap(Eg?5.0 e V),and has excellent thermal stability(>650?).The band gap of Y(HSe O₃)(Se O₃)(H₂O)·(H₂O)is 4.96 e V.This compound is stable below 133?.Both of these two compounds can achieve I-type phase matching.