Structure, chemistry and synthesis of non-linear optical materials

Chalcogenide glasses are known for their IR transparency and high nonlinear properties.; The structure of the glasses is studied to understand the origin of their optical properties. Both bulk and film glasses are studied to pinpoint the variation in their structure as a major variable that influences their properties. X-ray Photoelectron Spectroscopy (XPS) and Extended X-ray Absorption for Fine Structure (EXAFS) techniques are used, and the results are compared with Raman studies. According to a model by Lucovsky, chalcogen-rich As(S,Se) is made of arsenic pyramidal structural unit AsS₃ (AsSe₃), which are connected through chalcogen chain between them. Our results show that in As-S-Se glasses, S mainly stays in the AsS_3/2 units, while Se stays in the chains, forming homopolar bonds. This result supports the previous conclusion that the high nonlinearity in chalcogen-rich As-S-Se are related to the chalcogen homopolar bonds. According to the valence band XPS results, with the increase of Se in As-S-Se glasses, a noticeable decrease in the electronic band gap was observed. This further provides insight into the structural origin of the optical band red shift with increased Se composition.; Furthermore, the environmental effects on arsenic chalcogenide glasses are also studied for their potential outdoor applications. XPS, Raman and Fourier Transform Infra Red Spectroscopy (FTIR) confirmed no obvious structural or chemical changes at high temperatures in ambient atmosphere. The only observed degradation is the slight increasing in the surface roughness as shown by Atomic Force Microscopy (AFM). The overall conclusion is that the chalcogenide components can withstand adverse atmospheric conditions without changing their optical properties for a long period of time.; Since the processing conditions play a major role in fabricating optical materials, a modified sol-gel process was adopted as an alternative route for synthesis of optical materials with high nonlinearity. Sol-gel process was selected for easy control of chemical composition through proper choice of precursors and its cost effectiveness. The nano-metal doped glass systems are known for their high nonlinearity. These films are prepared by sol-gel and subsequently optical and structural properties are studied using XPS, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), RBS and AFM. The results showed that both particle size and optical properties can be controlled readily through simple heat-treatments. (Abstract shortened by UMI.)...