Syntheses And Characterization Of Compounds With Mixed Anions Of Germanate

Mid infrared laser has significant role in national defense,medical treatment,communication and laser processing.However,the main ways for all-solid-state lasers to obtain mid infrared lasers is that nonlinear optical crystals expand the mature laser to the mid infrared through the frequency conversion.Therefore,the development of infrared nonlinear optical crystal is of great significance to promote the development of mid infrared all-solid-state laser technology.Previous studies have shown that chalcogenide compounds,metal oxides and halides are the three classical material systems for design of mid infrared nonlinear optical crystal,and they possess their own advantages and defects.Hence,it is difficult for a single material system to fully meet all the performance requirements of nonlinear optical crystals.On the contrary,combining multiple anion elements is an effective strategy for design and synthesis new nonlinear optical crystals.So,a series of new nonlinear optical crystals have been successfully designed and synthesized by combining two anions,such as:Ba₃AGa₅Se₁₀Cl₂（A=Cs,Rb,K）,Pb₁₇O₈Cl₁₈,Bi FSe O₃,Ba Ge OSe₂ect.However,there is still no report that a material is simultaneously composed of three anions.In this thesis,in the first step,we explored two anionic chalcohalides and oxy-chalcogenides,and synthesized a series of new crystals of chalcohalides and oxy-chalcogenides compounds with two anionic.Then,based above on guidance,we successfully designed and synthesized the first compound with three anions-Ba₂F₂Ge₂O₃S₂.The crystal is composed of[Ba₂F₂]layered structure and[Ge OS]layered structure to form an aurivillius-type three-dimensional structure,and crystallizes in a non-centrosymmetric Aba2 space group.The property characterization results show that the compound possess big second harmonic generation response:1.4×Ag Ga S₂;relatively wide infrared transmission range:9μm;large optical band gap:4.45e V.In addition,the material also has moderate birefringence,which can ensure the phase-matching ability of the material in a relative wide wavelength range.Therefore,the compound is not only a potential mid infrared nonlinear optical crystal,but also provides a new idea for the design and synthesis of mid infrared nonlinear optical crystals with big second harmonic generation response,large band gap and suitable birefringence.And the innovation of the research work is as follows:1)Nine polyanionic compounds were designed and synthesized,crystal structures were determined by single crystal X-ray diffraction,there be linear and nonlinear optical properties were studied based on these characterization of infrared,Raman,diffuse reflection and powder second harmonic generation response.2)Ba₂F₂Ge₂O₃S₂ is the first multi-anion mid-infrared nonlinear optical crystal simultaneously containing three anions.The compound exhibits good nonlinear optical performance and will be potential applications in mid- infrared laser output.