| Chalcogenide glasses are well-known and promising materials for a variety of photonic applications such as ultrafast all-optical switches, frequency converters, optical amplifiers, infrared lasers and infrared transmitting optical fibers, covering the civil, medical and military areas. The interest in these materials stems principally from their low phonon energy, extended infrared transparency, high refractive index, high photosensitivity, ease of fabrication and processing, good chemical durability and special second/third-order optical nonlinearity.In this thesis, substantial efforts have been put into the fabrication, structure and properties of a new series of homogeneous chalcogenide glasses in the GeS2-Ga2S3-CdS pseudoternary system for the first time to the best of our knowledge. They were fabricated by the conventional melt-quenching technique, and characterized by X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSC-TG), visible-IR transmission, Raman spectroscopy and femtosecond time-resolved optical Kerr gate technique, together with chemical durability, refractive index and density measurements.The results show that the glass-forming region is mainly situated in the GeS2-rich domain and the amount of dissolved CdS is up to over 30 mol%. The obtained bulk glasses are homogeneous and have relatively high glass transition temperatures (338-436 C), strong thermal stabilities, good chemical durability, broad transparencies (0.45-11.5 m), large refractive indices (2.01-2.25) and large densities (2.68-3.18 g cm-3). The long-wavelength cutoff edge is found near 12 um due to the multiphonon Ge-S and Ga-S vibrations. They also exhibit large and ultrafast third-order optical nonlinearities compared with oxide glasses. These glasses may be widely used in the field of optoelectronics.In GeS2-Ga2S3 glasses, the basic structural units forming the backbone ofthe network are GeS4/2 and GaS4/2 tetrahedra which are connected through a bridging sulfur to form a three-dimensional network. A part of these tetrahedra is also connected via metal-metal homo-bonds which are Ge-Ge and Ga-Ga bonds. Most of GaS4/2 tetrahedra are edge-shared. Ge2+ ions may surround [GaS4/2]1- tetrahedra acting as charge compensators. Upon the addition of CdS into the GeS2-Ga2S3 system, the number of the metal-metal bonds and edge-shared GaS4/2 tetrahedra decreases, resulting in the formation of corner-shared tetrahedra with non-bridging sulfurs (NBS). Cd2+ ions can be dissolved into the glass network as charge compensators for these NBS and existed few [GaS4/2]1- tetrahedra. The high solubility of CdS is ascribed to the dissociation of metal-metal bonds and edge-shared tetrahedra in these Ga-containing glasses. The compositional dependences of some properties were detailed discussed by making reference to the structural variation on the basis of Raman scattering data. The existed metal-metal bonds, stability of the structural units and type of their interconnection (corner shared or edge shared) have the significant impact on their properties.The optimum glass composition for practical use in this system is 90GeS2-5Ga2S3-5CdS (in mol%). It has large density (-2.83 g cm-3), large refractive index (-2.12), high glass transition temperature over 430 C, a broad region of transmission from 0.46 to 11.5 m, good thermal stability for drawing optical fibers, and excellent chemical durability in normal air conditions as well as in distilled water. The third-order nonlinear susceptibility is estimated to be as large as 1.0 10-12 esu at 820 nm. The full width at half maximum (FWHM) of the Kerr signal is 150 fs, implying that the sample has a response faster than 120 fs which is limited by the laser pulse width. Its response is dominantly assigned to the ultrafast distortion of the electron cloud. This glass sample is potentially useful in future all-optical switching devices.
|
PDF Full Text Request