Optical and electronic characterization of sol-gel-derived silica aerogels for display and imaging applications

Aerogels are a unique class of ultra low-density solid materials with interconnected pores and porosities up to 98%. Their nanometer-sized structures create remarkable optical, electrical, and structural properties. This dissertation focuses on the optical and electronic properties of silica aerogels foruse in display and imaging applications. Thus the absorption and emission bands of aerogels, the aerogel's response to free electrons, and electric field effects on silica aerogels have been investigated. In addition, secondary electron emission has been proposed for aerogels. Finally, inorganic- and organic-doped aerogels were also studied to help determine the suitability of silica aerogels as a host matrix.; An adequate host material for an electroluminescent display must meet the following four requirements. First, the host material must have a large enough bandgap to allow visible light emission from the doped luminescent centers and limited luminescence by the host material where the doped luminescent centers emit light. Second, the host material must allow efficient transport of high energy (>2 eV) electrons, to create luminescence in the luminescent centers. Third, the host material must be able to withstand a high electric field without electric breakdown. And, fourth, the host material must not interfere with the desirable dopant properties. This dissertation shows that aerogels do meet these requirements.; Optical spectroscopy is used as the primary study tool and results are discussed in terms of implications for the optical and electronic structure of aerogels as well as similarities and differences with normal density amorphous silica. The differences are due to the unique nanostructure and large interconnected pores of aerogels created by their extremely low densities. Cathodoluminescence data and current-voltage characteristics of low-density silica aerogels are presented to evaluate their potential performance in electroluminescent devices. Evidence for Fowler-Nordheim tunneling of electrons into the aerogel matrix is found. Additionally, the attractive phenomenon of electron multiplication is examined and explained in terms of the aerogel's novel microstructure. The results demonstrate the utility of silica aerogels as unique, multifunctional host matrices for organic and inorganic luminescent materials for display and imaging applications.