Investigations On Synthesis And Properties Of Novel Alkali(Alkaline Earth) Metal Chalcogenide Nonlinear Optical Materials

In many scientific and technological fields,the infrared nonlinear optical crystal has important effect on the generation of mid infrared coherent laser light source.However,the existing mid infrared nonlinear optical crystals,such as AgGaQ₂(Q=S,Se)and ZnGeP₂,have the problem of low laser damage threshold,which makes their applications in high power applications severely hampered.It is well known that the intrinsic reason for the low laser damage threshold of these crystals is their narrow band gap.Therefore,to find a new kind of crystal with a large band gap(more than 3 eV)has become one of the great challenges to the field.This paper took chalcogenides as the research object,introducing alkali metals,alkaline earth metals,systematically studied the new infrared nonlinear optical crystal materials.The main research contents and results are as follows:1,Synthesized and studied the linear and nonlinear properties of Li GaGe₂S₆.The compound LiGaGe₂S₆ crystallizes in the orthorhombic space group Fdd2(NO.43)with lattice parameters a=11.925(2)?,b=22.647(5)?,c=6.8308(14)?,Z=8.The structure of compound LiGaGe₂S₆ is composed by dimeric[Li₂S₇]?trimeric[Ge₃S₁₀]and[GaS₄]tetrahedral through corner-sharing to form a three-dimensional framework.LiGaGe₂S₆ possesses the lowest Li content and the lowest melting point(663?)in Li-containing compounds.The band gap of LiGaGe₂S₆ is 3.53eV measured by UV vis diffuse reflectance spectroscopy.At the same time,it processes great NLO effect(50×KDP)and the LDT of it is about 6 times of AgGaS₂.2,Synthesised and studied a new type of chalcogenide nonlinear material NaSb₃GeS₇ and its crystal structure.The compound NaSb₃GeS₇ crystallizes in the hexagonal space group P6₃(NO.173)with lattice parameters a=10.0853(13)?,b=10.0853(13)?,c=5.7551(8)?,Z=1.The structure of compound NaSb₃GeS₇ is composed by trimeric[Sb₃S₉]and[GeS₄]tetrahedral through corner-sharing to form a three-dimensional framework,and all the Na atoms are located inside the cavities.The theoretical calculation shows that the band gap of NaSb₃GeS₇ is 2.126 eV,and the material has very large nonlinear optical effect,which is about 50 times of KDP.3,Synthesized and studied the crystal structure and its negative thermal expansion property of the new compound KYGeS₄.The compound KYGeS₄ crystallizes in the monoclinic space group P2₁(NO.4)with lattice parameters a=6.428(6)?,b=6.641(6)?,c=8.612(8)?,Z=2,with lamellar structure consisting of edge and corner-sharing[YGe₄S₁₅]units formed by two[YS₇]units and two[GeS₄]tetrahedrons,the K⁺cations are resided in the tunnels between each layer to make a charge balance.The second harmonic generation(SHG)effect of KYGeS₄ is close to that of AgGaS₂,as confirmed by the first-principles calculations.Moreover,the diffuse reflectance spectra reveal that the energy band gap of KYGeS₄ is above 3.0 eV,larger than that of AgGaS₂(2.7eV).The birefringence of KYGeS₄ is predicted to be 0.11 at the wavelength of 1?m,which is enough to achieve the phase-matching condition for SHG production in the mid-IR region.Through thermal analysis,we found that it has negative thermal expansion property,that is to say,its axial length shorten with the increase of temperature.Our results demonstrate that KYGeS₄ may possess improved optical properties compared with AgGaQ₂(Q=S,Se)and is promising for application as a good IR NLO material.4,Synthesized chalcogenide alkaline earth metal compounds:BaAl₄S₇?Ba₄Ga₂S₇?Ba₆Zn₆HfS₁₄?Ba₄Zn₄Y_1.33S₁₀.The compound BaAl₄S₇ crystallizes in the orthorhombic space group P2₁nm(N0.31)with lattice parameters a=5.8685(3)?,b=6.2040(4)?,c=14.7485(8)?,Z=2.The structure of BaAl₄S₇ is very simple which is a three-dimensional framework consisting of corner-sharing[AlS₄]and all the Ba atoms are distributed in the tunnel through the connection of covalent bond with S atoms.The two crystals of Ba₄Ga₂S₇ crystallize in the monoclinic with different space group.?-Ba₄Ga₂S₇ crystallizes in P 2₁/m(No.11)with lattice parameters a=9.0109(13)?,b=7.1350(9)?,c=11.6984(15)?,?=108.231(3)°,Z=2.?-Ba₄Ga₂S₇ crystallizes in C2/m(N0.12)with lattice parameters a=24.645(3)?,b=6.8381(8)?,c=8.9413(10)?,?=104.107(3)°,Z=12.The structure of?-Ba₄Ga₂S₇ is constructed from isolated dimeric[Ge₂S₇]units connected by two[GeS₄]tetrahedrons through corner-sharing,and all the Ba atoms are located in the gap between these two isolated units.In the structure of?-Ba₄Ga₂S₇,not only have isolated dimeric[Ge₂S₆]units linked by two[GeS₄]tetrahedrons through edge-sharing but isolated[GeS₄]units,and Ba atoms are located in the gap between these two isolated units.The compound Ba₆Zn₆HfS₁₄ crystallizes in the tetragonal space group I4/mcm (N0.140)with lattice parameters a=16.4037(11)?,b=16.4037(11)?,c=9.7524(7)?,Z=4.The structure of Ba₆Zn₆HfS₁₄ is composed of several isolated parts.Among them,[HfS₆]hexahedrons connect to each other one by one by corner-sharing along the c direction and form a two-dimensional single chain.[ZnS₄]tetrahedrons consist a three-dimensional framework by corner or edge-sharing.All the Ba atoms are distributed in the tunnel formed by the two-dimensional single chain and the three-dimensional framework.The compound Ba₄Zn₄Y_1.33S₁₀ crystallizes in the monoclinic space group C2/m (No.12)with lattice parameters a=13.786(2)?,b=4.0787(7)?,c=9.5163(15)?,Z=4.The structure of Ba₄Zn₄Y_1.33S₁₀ is a layer which is composed by the units of[Zn₂YS₁₀],and all the Ba atoms are located between the two layers.