Synthesis,Structure And Properties Of Metal Beryllium Borate And Silicate Ultraviolet Optical Crystals

With the rapid development of UV all-solid-state lasers,it is necessary to explore new UV optical crystal materials.To synthesize ultraviolet optical crystals materials with wide optical bandgap,in this dissertation,we introduce Be O₄ tetrahedra,Si O₄ tetrahedra,stereochemically active lone pair cations,and alkali or alkaline-earth cations which are free of d-d or f-f electronic transitions into beryllium borate and silicates through high-temperature solid-state synthesis method.New UV optical crystal materials were successfully obtained.The structure and performance of them are discussed and analyzed as follows:(1)Two new metal beryllium borates Zn Be₂B₂O₆ and Na Mg_0.5Zn_0.5Be₂B₂O₆F were successfully designed and synthesized.Zn Be₂B₂O₆ crystallizes into an orthorhombic space group Pbcm(No.57),which is a new type of double-layer structure bridged by BO₃ groups.It features a 3D framework constructed by[Be₈B₆O₂₂]?double layer bridged by BO₃ groups.BO₃ groups are connected to Be O₄ tetrahedrons via corner-sharing O atoms to form a 2D[Be₄B₂O₁₁]?layer.The adjacent[Be₄B₂O₁₁]?layers are linked via B(3)O₃ groups to create the[Be₈B₆O₂₂]?double layers,which are further bridged via B(1)O₃ groups,generating the 3D framework with two types of tunnels filled by Zn²⁺.In addition,we introduce alkali metal,alkaline earth-metal and highly electronegative F^-into parent Zn Be₂B₂O₆ to produce new Na Mg_0.5Zn_0.5Be₂B₂O₆F,crystallizing into a trigonal space group P-31c(No.163).The BO₃triangles and Be O₃F tetrahedra are connected by sharing bridging O corners to produce a two-dimensional[Be₃B₃O₆F₃]?layer.In particular,the[Be₃B₃O₆F₃]?layer is held together with another adjacent layer reversely through bridging fluorine atoms,forming a unique[Be₆B₆O₁₂F₃]_?double layers with a series of tunnels where Na⁺cations reside in the channels.Mg²⁺/Zn²⁺cations are located in the space between two neighboring[Be₆B₆O₁₂F₃]_?double layers.The compound not only maintains the similar layer structure of KBBF and SBBO,but also reduces the interlayer distance,which is beneficial to enhance the interlayer force.The thermal properties of both compounds show that both compounds have good thermal stability.Optical measurements reveal that they have short UV cut-off edges(<250 nm)in which UV cut-off edge of Na Mg_0.5Zn_0.5Be₂B₂O₆F is shorter than that of Zn Be₂B₂O₆,showing that they are potential ultraviolet optical crystal materials.(2)Two new metal silicates Rb₂Pb₂Si₂O₇ and Rb₂Ca₄Si₆O₁₇ were successfully synthesized.Rb₂Pb₂Si₂O₇ crystallizes in a trigonal space group P-3(No.147),which possesses[Pb₃Si₃O₉]_?layers constructed by corner-sharing connections of Si O₄ tetrahedrons and Pb O₃ groups.The adjacent[Pb₃Si₃O₉]?layers are linked via corner-sharing to generate[Pb₆Si₆O₁₈]_?double layers,which are separated by Rb⁺.Rb₂Ca₄Si₆O₁₇ crystallizes in a triclinic space group P-1(No.2),which exhibts the double layers composed of corner-sharing connections of Si O₄ tetrahedra and Ca O_n(n=6,7)polyhedra.The double layers are further connected to generate 3D structure with two types of channels filled by Rb⁺.The thermal properties show that they all have good thermal stability.Optical properties of the both compounds reveal that they can reach the UV region in which UV cut-off edge of Rb₂Ca₄Si₆O₁₇ is shorter than that of Rb₂Pb₂Si₂O₇,showing that the crystals could have an potential application as ultraviolet optical crystal material.