Research On Synthesis,Structure And Properties Of Novel Borate/Phosphate Second-Order Nonlinear Optical Materials

With the development of optical communication,atmospheric environment monitoring,minimally invasive surgery,laser processing,laser guidance,and other fields of technology and scientific research,the research of second-order nonlinear optical crystal materials has drawn more and more attention.And the demand for these materials is becoming more and more urgent.In this thesis,the main goal is to explore new nonlinear crystal materials by high temperature solution and solid-state methods.We select active units(anionic groups:B-O,P-O and V-O groups,cations:alkali metals,alkaline earth metals,rare earth metals,lone-pair and d¹⁰ transition metals)that are favorable for broadening the transmission range or benificial to second-harmonic generation?SHG?.Multiple rare-earth borates and polyphosphates compounds have been synthesized.The main research contents are as follows:?1?K₇MRE₂B₁₅O₃₀?M=Zn,Cd,Pb;RE=Sc,Y,Gd,Lu?:Synthesis and characterization of a series of rare earth metal borates with potential applications in the nonlinear field.Almost 20 new compounds K₇MRE₂B₁₅O₃₀?M=Zn,Cd,Pb;RE=Sc,Y,Gd,Lu? have been synthesized by high-temperature solid state method,among which K₇MRE₂B₁₅O₃₀?M=Zn,Cd,Pb;RE=Sc,Y,Gd,Lu?crystallize in the trigonal system,and space group R32.All kinds of B atoms connect with O atoms to form BO₃ triangles and BO₄ tetrahedra,and they link together to form the B₅O₁₀ groups via corner sharing.Then the B₅O₁₀ groups share four vertical O atoms with neighboring REO₆ octahedra to form a three-dimension?3D?framework.The K⁺and M²⁺cations are located in the cavities to keep charge balance.The UV–Vis–NIR diffuse reflectance spectra show that K₇CdRE₂B₁₅O₃₀?RE=Sc,Y,Gd,Lu?have no obvious absorption in the UV-Vis-NIR region,and the cut-off edges are about 200 nm.The selected compounds show that the powder SHG intensities range from 1.5².1 times that of KDP by a Q-switched Nd:YAG laser at 1064 nm,and are phase-matchable.In addition,the theoretical calculation was employed for better understanding the structure–property relationships.?2?LiZnP₃O₉:Crystal structures and theoretical studies of a polyphosphate for nonlinear optical applications.LiZnP₃O₉ crystallizes in the orthorhombic space group P2₁2₁2₁ with unit cell parameters a=8.330?3??,b=8.520?3??,c=8.635?3??,and Z=4.In the structure,all the P atoms are coordinated by four O atoms forming the PO₄ tetrahedra and further connected to generate a zig-zag[PO₃]_?anionic framework.Li atoms and Zn atoms are filled in the gap of formed by[PO₃]_?chains.The UV–Vis–NIR diffuse reflectance spectrum indicates that LiZnP₃O₉ has a short cutoff edge at about 204 nm.LiZnP₃O₉ exhibits an SHG efficiency about 0.2 times that of KDP by a Q-switched Nd:YAG laser at 1064 nm,and is phase-matchable.In addition,the first-principles calculation was employed for better understanding the structure–property relationships of LiZnP₃O₉.