Exploration Of NLO And Birefringence Crystals With Lone Pair Electron Cation(Bi³⁺?Pb²⁺)

Nonlinear optical(NLO)crystals have been attracting more and more interest because they can be used in laser frequency conversion,optical parametric oscillation,laser ranging optical communication and so on.In the process of exploring nonlinear optical crystal with excellent performance,it is the long-term challenge to balance the contradiction among the three important indexes,including second harmonic generation(SHG)effect,band gap and birefringence.The main work of this thesis was to explore new NLO crystals,especially the compounds containing lone pair electron cations(Pb²⁺?Bi³⁺).The main ideas are as follows:(1)in the sulfate system,the lone pair electron Bi³⁺cation was introduced to explore sulfate crystal with large SHG effect and moderate birefringence;(2)in carbonate,the largest electronegativity F^-ion and lone pair electron Pb²⁺cation were introduced to obtain fluorocarbonate with large birefringence.A₂Bi₂(SO₄)₂Cl₄(A=NH₄,K,Rb)and NaPb₂(CO₃)₂F_x(OH)_1-x(0<x?1)crystals were synthesized.1.The synthesis and properties of sulfate with lone pair electron Bi³⁺cationA series of A₂Bi₂(SO₄)₂Cl₄(A=NH₄,K,Rb)crystals were prepared by saturated solution evaporation.The space groups of A₂Bi₂(SO₄)₂Cl₄(A=NH₄,K,Rb)were all P2₁2₁2₁ with noncentrosymmetric,and the powder SHG effects were 4.8,5.5,and 5.3×KDP,respectively.The theoretical birefringence was 0.055,0.056 and 0.047 at 1064nm for A₂Bi₂(SO₄)₂Cl₄(A=NH₄,K,Rb),respectively.The first principle calculations illuminated that of large SHG effect and moderate birefringence derived from the synergistic effect of BiO₅Cl₂ polyhedron and SO₄ tetrahedron.2.The synthesis and properties of fluorocarbonate containing lone pair electron Pb²⁺cationNaPb₂(CO₃)₂F_x(OH)_1-x was obtained by hydrothermal method,and crystallized space group P6₃/mmc.The UV spectrum showed that its band gap was 4.28e V,and the birefringence measured by polarizing microscope was 0.275,which is a potential UV birefringence crystal.The calculation showed that the outstanding birefringence mainly orginated from[CO₃]^2-group and lone pair electron Pb²⁺cation.