Synthesis,Structure And Properties Of Alkali/Alkaline Earth Metal Yttrium Borate

Ultraviolet,especially deep ultraviolet laser has important applications in laser micromachining,high-density optical storage and laser lithography,and nonlinear optical crystals and birefringent crystals are the core basic materials for solid-state lasers to output ultraviolet laser and realize laser modulation.In this study,borate is selected as the main research object aiming at the design and synthesis of new ultraviolet nonlinear optical crystals and birefringent crystals.By introducing easily polarized Y-O unite and halogen anion with large electronegativity into borate,10 new alkali/alkaline earth metal yttrium borate crystals have been successfully designed and synthesized.Their crystal structures were determined by single crystal X-ray diffraction,and their linear,nonlinear and thermal properties were systematically studied by infrared,thermogravimetric,diffuse reflection and powder second harmonic generation(SHG)measurements.The results show that Ba YOBO₃ is a potential nonlinear optical material in ultraviolet and deep ultraviolet due to its SHG response and short ultraviolet(UV)cutoff edge.Li₂MY₄B₅O₁₅(M=Rb,Cs)and K₂YB₃O₆F₂ show large birefringence and have potential applications in UV and deep UV laser modulation.The main achievements and innovations are summarized as follows:1.BaYOBO₃:a deep UV nonlinear optical crystal was designed,synthesized and characterized.BaYOBO₃ is very similar in structure to KBe₂BO₃F₂(KBBF)which is the only practical nonlinear optical crystal(NLO)in deep ultraviolet region.And it can be regarded as substituting Be²⁺with Y³⁺from KBBF to avoid the use of highly toxic raw material Be O.Meanwhile,different from the layered structure of KBBF,the Ba YBO features a stable three-dimensional framework by sharing O,which is conducive to crystal growth.Finally,we further obtained compound Ba YOBO₃,which is a potential deep ultraviolet nonlinear optical crystal with a size of 8 mm×5mm×4 mm.The results show that it a large SHG response(?2.6×KDP)and a short UV cut-off edge(<190 nm)as a promising deep-UV NLO candidate.2.Li₂MY₄B₅O₁₅(M=Rb,Cs):deep birefringence crystals were designed,synthesized and characterized.The introduction of Y-O group into borate system is also beneficial to enhance the anisotropy of materials,thus it can effectively improve the birefringence of materials.Based on the consideration,we successfully synthesized two birefringent crystal materials Li₂MY₄B₅O₁₅(M=Rb,Cs)with deep ultraviolet transmission region.Their birefringence values are 0.103 and 0.104 at 532 nm,respectively,and the UV cut-off edge are less than 190 nm.The electron population is calculated by LCAO-MO Molecular Wave Functions and we successfully explain the source of the large birefringence in material.The introduction of Y-O group into borate system offers a new point of view on designing borates with desirable birefringence values.3.Design,synthesis and characterization of yttrium borate containing halogen.The introduction of halogen into the structure can further broaden the transmission range of the material and enhance the structural anisotropy,but the rare earth borate is difficult to be introduced into rare earth borate because of its high synthesis temperature and volatile halogen.In the research,we reduced the melting point of the material by selecting suitable flux and successfully obtained two rare earth borates containing halogen(Ba₂YB₂O₆Br and K₂YB₃O₆F₂).They also have large birefringence,0.08 and 0.12,respectively.And the UV cutoff edge is shorter than 190nm,so they are potential birefringent crystal materials.