Study On Formation, Structure And Properties Of Nonlinear Optical Glasses In The GeS₂ Systems

Nonlinear optical glasses have received great interests owing to their potential wide applications in the fields of optical communication, modulation, transferring, and etc.. Chalcogenide glasses have larger nonlinear optical coefficient than ordinary oxide glasses, therefore, become new attractive subject. In this thesis, two novel GeS₂-Ga₂S₃-PbI₂ and GeS₂-Sb₂S₃-CdS pseudo-ternary systems were prepared by melt-quenching technique. Utilizing the techniques such as EPMA, XRD, Raman, DSC-TG, UV-Vis-IR, FT-IR and so on, the relationships between composition, structure and properties of the glasses have been studied systematically. Utilizing the femtosecond time-resolved optical Kerr shutter (OKE) and Maker fringe methods, the third-order nonlinear optical property and second-harmonic generation (SHG) of the glasses after electrically/thermally poled have been analyzed, including their dependences on composition and structure. The aim of this work is to search new nonlinear optical material with high performance and offer reference for its further improvement.The glass-forming region of GeS₂-Ga₂S₃-PbI₂ system is determined. The glass transition temperatures range from 252.5～398.5℃and the composition with the best formation ability is 0.72GeS₂·0.18Ga₂S₃·0.1PbI₂. These glasses have high refractive indices (n_D=1.95～2.36) and dispersion (v=11.15～14.50), large densities (d=2.712～3.825g·cm^-3) and microhardness (H_v=172.3～266.5kg·mm^-2). In the transmission region 0.5 to 12.7μm, the transmittance is higher than 70%. The basic structure units forming the glass network are [GeS₄], [GAS₄] tetrahedra and [S₃GeI], [S₂GeI₂], [S₃GaI] mixed-anion tetrahedra, which are connected by comer-shared or edge-shared mode through bridging sulfurs and/or short S-S chains to form a three-dimensional network. In the glasses with little PbI₂, some part of [S₃Ge-GeS₃], [S₃Ga-GaS₃] ethane-liked units exist, but they will be dissolved with the addition of PbI₂. The defects of glasses derive from the non-stoichiometry of composition and the depolymerization of PbI₂.The glass-forming region of GeS₂-Sb₂S₃-CdS system is determined. The glass transition temperatures range from 293.0～310.0℃and the composition with the best formation ability is 0.7GeS₂·0.3Sb₂S₃. These glasses have high refractive indices (n_D=1.95～2.43) and dispersion (v=8.24～14.50), large densities (d=2.99～3.29g·cm^-3) and microhardness (H_v=158.9～250.9kg·mm^-2. In the transmission region 0.5 to 12μm, the transmittance is higher than 60%. the basic structure units forming the glass network are quasi-three-dimensional (3D) [GeS₄] tetrahedra and quasi-two-dimensional (2D) [SbS₃] pyramids. With the increase of Sb₂S₃, the structure of glass transfer from the 3D structure to the [GeS₄]_m, [SbS₃]_n, formed layer or chain structure, which are inerconneeted by Ge-S-Sb bridging sulfur and Sb-Sb, Ge-Sb, Ge-Ge metallic bonds. CdS can bring some non-bridge sulfur with NBS and decrease the degree of aggregation. Because of the additionss of Sb₂S₃ and CdS, large amounts of metallic and dangling bonds are formed, therefore, the defects of glass are enhanced.GeS₂-Ga₂S₃-PbI₂ and GeS₂-Sb₂S₃-CdS glasses have large and ultrafast (～100fs) third-order optical nonlinearity. The largest X⁽³⁾ of GeS₂-Ga₂S₃-PbI₂ is 2.07×10^-13esu, and the relationship of X⁽³⁾ and the linear refraction index n does not obey the Miller rule. The ultrafast third-order nonlinear optical responses mainly originate from the distortion of electron cloud of Ge-S and/or Ga-S bonds. The largest X⁽³⁾ of GeS₂-Sb₂S₃-CdS is 8.30×10^-13esu, and the relationship of X⁽³⁾ and the linear refraction index n obeys the Miller rule. The distortion of electronic cloud of Sb³⁺ under large electric field has dominant effect on the third-order nonlinearity. Some approachs can effectively enhance X⁽³⁾, such as increasing the connection of structure units, reducing the defects and introducing ions with large polarizability into glass network.Maker-fringes with good symmetry have been observed within the GeS₂-Ga₂S₃-PbI₂ and GeS₂-Sb₂S₃-CdSglasses after electrical/thermal poling. The second-order optical nonlinearity have tight relation with poling conditions, glass composition and structure, and the mechanism can be explained by dipole reorientation model. Under the poling condition conducted with 6kV, 250℃and 40min, the maximum of second-order nonlinear susceptibility X⁽²⁾=4pm/V for 0.7GeS₂·0.15Ga₂S₃·0.15PbI₂ glass and X⁽²⁾=9pm/V for 0.85GeS₂·0.1Sb₂S₃·0.05CdS glass, respectively. It was found that the effective poled region is located at several microns under surface of anode and the SHG have good durability at room temperature.