Preparation And Performance Study Of Ultraviolet Optical Crystals For Borosilicate/borate And Phosphate Fluoride

Photoelectric functional crystal materials have become a hotspot in the material science and engineering field due to their wide application in laser and optoelectronics.In order to explore new photoelectric functional crystal materials,this thesis proposes research ideas for designing and synthesizing new materials in borosilicate,borate and phosphate fluoride systems based on the research status of photoelectric functional crystal materials at home and abroad.A series of UV optical crystals were successfully synthesized by high temperature solution method.Besides,the performance and theoretical calculations of these compounds were carried out.The main results are as follows:1.CsBSi₅O₁₂By introducing SiO₄ into borate,a noncentrosymmetric CsBSi₅O₁₂ single crystal is obtained by the high temperature solution method in the closed system.Using single crystal X-ray diffraction techniques,we collected single crystal data for this compound.It has a zeolite-like structure:Si/BO₄ tetrahedrons are connected by a shared oxygen into a three-dimensional structure with two kinds size tunnels,which extend along the c-axis,in which Cs atoms are filled in large tunnels to maintain charge balance,there is no Cs atom filling in the tunnels.Furthermore,we conducted detailed structural comparisons,including CsBSi₅O₁₂ and other reported Cs borosilicates,CsBGe₅O₁₂.In addition,we characterized its optical properties including infrared spectroscopy,diffuse reflectance spectroscopy,and powder SHG effect.Its SHG effect is about 0.2 times KDP.The diffuse reflectance spectrum shows that the UV cutoff edge is below 200 nm,which means that the compound may have some use in the deep ultraviolet region.Meanwhile,we use first-principles calculations to reveal sources of linear and nonlinear optical properties.2.RbBSi₂O₆The single crystal of the isomorphous I4?3d phase RbBSi₂O₆ is prepared by high temperature solution method.Its crystal structure is determined by single crystal X-ray diffraction technique.The compound has a leucite-related structure:Si/BO₄ tetrahedrons are connected by sharing oxygen atom to form a three-dimensional structure containing tunnels and cavities,and Rb atoms are filled therein.Excepting the powder polycrystalline of RbBSi₂O₆,we also synthesized powder polycrystalline of the same stoichiometric CsBSi₂O₆,and carried out IR and UV-Vis-NIR spectra measurement of two compounds.Diffuse reflectance spectroscopy shows that the UV cutoff edge of RbBSi₂O₆ is lower than 180 nm,and the UV cutoff edge of CsBSi₂O₆ is lower than 185 nm,indicating that they have some application possibilities in the deep ultraviolet region.In addition,we also calculated the band structure and partial density of states of RbBSi₂O₆.3.A₂CaPO₄F?A=K,Rb?Two alkali metal-alkaline earth metal mixed phosphate fluorides,A₂CaPO₄F?A=K,Rb?,were successfully synthesized by a high temperature solution method.Two compounds are isomorphic to each other and belong to the Pnma space group of the orthorhombic system.Their three-dimensional structure is consisted of the 1D infinitely extended zig-zag[FA₂Ca]chains interlinked by isolated PO₄ groups.The zig-zag chains in the structure that composed of plane-sharing the[FA₄Ca₂]octahedra along the c direction belong to 1D perovskite-like structure.At the same time,based on the cation size effect,we have analyzed the regulation of the alkaline earth metal cations on the frameworks of perovskite-like structures in the A₂MPO₄F?A=K,Rb;M=Ba,Ca?.In addition,the diffuse reflectance measured results show that the UV cutoff edges of K₂CaPO₄F and Rb₂CaPO₄F are lower than 242 and 248 nm,respectively,which means they may be used in the field of ultraviolet optics.In addition,using first-principles calculations studied the relationship between electronic structure and optical properties.4.Rb₄Pb₂B₇O₁₄FA new and rare alkali metal and lead borate fluoride,Rb₄Pb₂B₇O₁₄F,was successfully obtained.It crystallizes in the monoclinic P2₁/c space group,its intricate 3D crystal structure can be regarded as the layers consisted of RbO₇F and RbO₆F polyhedrons connected by isolated PbO₃,PbO₃F,and B₇O₁₄ groups.To the best of our knowledge,it is the fourth anhydrous borate containing only isolated B₇O₁₄.The first principle calculation results show that the compound has a indirect band gap,the calculated value of band gap is 4.18 eV;birefringence?n=0.026@1064 nm;Pb-O and B-O are the main contributors to its optical properties.5.LiRbB₈O₁₃A mixed alkali metal borate,LiRbB₈O₁₃,was successfully synthesized.Its structure contains two independent and interpenetrating 3D B-O frameworks formed by the basic building block?FBB?-B₈O₁₆group via shared oxygen atoms,while the cations Li⁺and Na⁺are reside in the tunnels and cavities.To the best of our knowledge,in the anhydrous mixed alkali metal borate,such compounds containing two independent and interpenetrating 3D B-O frameworks are few.The first principle calculation results show that LiRbB₈O₁₃ is an indirect band gap compound with a calculated band gap of 5.81 eV and the birefringence??n?is 0.08@1064 nm,indicating it may act as a birefringent crystal;its optical properties are result from B-O groups.