Synthesis, Structure And Properties Of Optical Crystals Containing Lone Pair Electrons Pb²⁺ And Sn²⁺

Photoelectric functional crystals,including laser crystals,electro-optic crystals,scintillation crystals,nonlinear optical crystals,birefringent crystals,etc.,are the material basis of the application and development of laser technology.Birefringent crystals can be used for laser polarization modulation,nonlinear optical crystals are mainly used for laser frequency conversion,is widely used in industrial production,laser communication,military weapons,laser medical treatment and scientific research and many other fields.The demand of photoelectric functional crystals is very large,and the existing crystals cannot meet the increasing demand of practical applications.Therefore,it is of great significance to carry out basic research on the design,synthesis and properties of new photoelectric functional crystal materials.In this paper,the borate and iodide systems are the research object.Through the closed system of high temperature melt method and hydrothermal method,we obtained[O2Pb3]2(BO3)I,KSnI3·H2O and NaB10O14(OH)4·(H3O)compounds.The synthesis,structure and optical properties of the three kinds of crystals were reported.The relationship between structure and properties was studied by the first principle calculations.The main contents are as follows:(?)A new lead borate iodide,[O2Pb3]2(BO3)I,has been successfully synthesized by a facile hydrothermal reaction.It exhibits an infinite one-dimensional(1D)?1[O2Pb3]double chain which constructs from the OPb4 oxygen-centered tetrahedra.The ?1[O2Pb3]double chains are further bridged by the BO3 units via sharing oxygen atoms to form two-dimensional(2D)?2[(O2Pb3)2(BO3)]layers with the I-ions situated in the spaces between the layers.First principles calculations indicate that[O2Pb3]2(BO3)I exhibits a birefringence of about 0.072@1064 nm which originates from the synergistic contributions of the Pb-O/I and BO3 units.(?)A new compound KSnI3·H2O was synthesized through the solid-state reaction method in a sealed quartz tube.KSnI3·H2O crystallizes in the centrosymmetric space group Pnma with lattice constants a=9.654(4)(?),b=4.6022(17)(?),c=20.466(8)(?),Z=4.In the crystal structure,The Sn(?)cations are five-coordinated with I-ions forming the special pyramidal SnI5 polyhedra which further condense to one-dimensional ?1[SnI3]chains connected by O-H…I hydrogen bonds and K-I bonds.Meanwhile,the first principles calculations indicate that the title compound exhibits a birefringence of about 0.121 at 1064 nm which is mainly originated from the contribution of the SnI5 polyhedra.(?)NaB10O14(OH)4·(H3O)crystals were obtained by by a facile hydrothermal reaction.The NaB10O14(OH)4·(H3O)is crystallized in the non-centrosymmetric space group P2/c,and the lattice constants are a=7.614(4)(?),b=8.970(4)(?),c=10.762(5)(?),?=103.764(6)°,Z=2.First-principles calculations show that the birefringence of the compound is 0.075@1064 nm and the band gap is 6.017 eV.The analysis of the density shows that the main contributor to the optical performance is the B-O anion framework.