Synthesis,Structure And Properties Of Deep-UV Phosphate And Borate Optical Crystal Materials

The synthesis of deep-UV optical crystal material has always been a hot spot for many researchers.Currently,the commercial deep-UV optical crystals which have a very important application in the medical,military and other fields are very lack.In this subject,four new crystal materials were synthesized in the two systems of phosphates and beryllium borates by high temperature solid-state reactions,and their structures,properties were studied.The results are as follows:First,introduced d¹⁰Zn²⁺into the Cs-Mg-P-O system,two new phosphate crystals,Cs₆Mg₆（PO₃）₁₈（CMP）and Cs₂MgZn₂（P₂O₇）₂（CMZP）were synthesized.We also synthesized their polycrystalline powder.CMP is a monoclinic,non-centrosymmetric and polar P21 space group with a = 7.7437（4）?,b = 34.1273（17）?,c = 10.1063（5）?,β = 90.414（2）?,V=2670.7（2）?3,Z = 2.The isolated MgO₆ octahedra and two one-dimensional [PO₃]∞ chains share oxygen atoms to form a new three-dimensional anionic framework.The second harmonic generation（SHG）response of the CMP polycrystalline powder is about 0.1 times that of KDP in the ultraviolet region,and it is phase-matchable.The dipole moment calculation suggests that the weak SHG response mostly originates from much distorted CsOn polyhedron.CMZP belongs to monoclinic,central symmetric P21/c space group,unit cell parameter is a = 13.5270（14）?,b = 7.4464（8）?,c = 14.6905（15）?,β = 90.746（4）?,V =1479.6（3）?3,Z = 4.The structure of the CMZP is characterized by a new [MgZn₂P₄O₂₀]14-structural unit consisting of two isolated P₂O₇ dimers,one ZnO₄ and two disordered Mg/ZnO₄ tetrahedral units.Their UV-visible diffuse reflectance spectra show that the UV cut-off edges are obviously below 190 nm,and their relationships between the electronic structure and the optical properties are elucidated by theoretical calculations.Second,in the Li₂O-B₂O₃-BeO system,Li₁₃Be₇B₉O₂₇ and Li₁₃MgBe₆B₉O₂₇ crystals withthe same molecular formula Li₁₃ABe₆B₉O₂₇ were synthesized,and both of them were crystallized in the hexagonal system P63/m space group.The unit cell parameter of Li₁₃Be₇B₉O₂₇ is a = 7.72789（19）?,c = 18.8399（6）?,V = 974.38（4）?3,Z = 2 while Li₁₃MgBe₆B₉O₂₇ has a unit cell parameter with a = 7.731 ?,c = 18.888 ?,V = 977.8 ?3,Z =2.Both of their structures contain new [Be6B9O33]∞ double anion framework,and Li+and A²⁺fill the space to balance charge.The only difference is that their structures belong to mirror symmetry.It is important to note that the two compounds contain a rare AO6 trigonal prism coordination environment（A = Be,Mg）,especially the unprecedented BeO₆ trigonal prism with ultralong Be-O bond length（2.2373（7）?）,which changes the convention that the Be-O group has only a strong covalent bond without the ionic bond.The optical tests show that their UV cutoff edges are below 190 nm,and the theoretical calculations show that their optical properties are mainly determined by the electron transition between the B-O and Be-O groups.Thermal stability analysis shows that they have excellent thermal stability.This indicates that the two beryllium borates have potential application in deep ultraviolet.