Synthesis And Poperties Of Birefringent And Nonlinear Optical Cystals Cntaining Lone Pair Electron Cations

Birefringent materials are the key devices for controlling light polarization in laser technology and optical communication.However,the current performance of commercial birefringent materials is limited by birefringent value,optical transmittance range,or the difficulty of attaining large size single crystals.For nonlinear optical materials,it is also necessary to explore new materials that can realize SHG and band gap balance.Through the screening of anionic groups,the system was introduced to contain stereochemically lone pair electrons(Se⁴⁺,Pb²⁺),the preliminary design and synthesis,and the subsequent performance characterization,the relationship between the structure and performance of the synthesized material was analyzed,and the origin of the performance was discussed.The specific research is as follows:（1）To explore new birefringent materials,we strategically incorporated a lone pair cation(Se⁴⁺)with large optical anisotropy,an alkali metal,and halogen ions(Rb⁺and Cl^-with superior UV transparent capacity;thus a new compound,Rb Cl·（H₂Se O₃）₂,was successfully discovered with the aid of the facile hydrothermal method.Interestingly,Rb-Cl chains locate in the[H₂Se O₃]∞skeleton,which makes Rb Cl·（H₂Se O₃）₂ a salt-inclusion selenite.Millimeter-sized single crystals（up to 4×2×1 mm³）were obtained,and the transmittance spectrum revealed that its UV cut-off edge can be as low as 230 nm.In addition,the calculated birefringence of Rb Cl·（H₂Se O₃）₂ is 0.14 at 589 nm that is similar to the birefringent value of famousα-Ba B₂O₄.Wide UV transparency,large birefringence,and feasible crystal growth make Rb Cl·（H₂Se O₃）₂a new member of birefringent materials for UV light applications.（2）By introducing lanthanide and alkali metals into the borate system,a series of new rare-earth borates Rb₇M^IIRE₂^IIIB₁₅O₃₀（M=Ca,Cd,Sr,Pb;RE=Y,La,Sm）were synthesized through solid-state and flux methods.The SHG of Rb₇Pb_0.59Sr_0.41La₂B₁₅O₃₀ reached 1.6×KDP due to the introduction of the lone pair cationic Pb²⁺.These compounds are isostructural and crystallize in the chiral noncentrosymmetric space group R32.Rb₇M^IIRE₂^IIIB₁₅O₃₀ exhibit a three-dimensional（3D）framework composed of[Rb O₆]octahedra,[Rb O₈]polyhedra,[REO₆]octahedra and[B₅O₁₀]polyhedra.Second harmonic generation（SHG）measurements at 1064nm on polycrystalline Rb₇M^IIRE₂^IIIB₁₅O₃₀ samples indicate that the compounds exhibit moderate SHG responses ranging from 0.7 to 1.6 times that of KH₂PO₄（KDP）at 1064 nm and are phase-matchable（type I）.In addition,their diffuse reflectance spectra reveal absorption edges change in the range of 314-350 nm,which indicate Rb₇M^IIRE₂^IIIB₁₅O₃₀ may have potential UV nonlinear optical（NLO）applications.