T. Suratwala

Sol—gel derived coatings on glass

Abstract Sol—gel processing is a versatile method for depositing oxide based coatings on a variety of substrates in an economical manner. The present review will consider coatings deposited on glass, and will discuss a number of representative applications for such coatings, namely anti-reflection coatings, transparent conducting coatings, anti-static coatings, fluorinated coatings, coatings incorporating active dye molecules and ferroelectric coatings.

Processing and photostability of pyrromethene 567 polycerams

Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with aQ-switched, frequency doubled Nd: YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm2. UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.

Photostability of silylated coumarin dyes in polyceram hosts

Numerous silylated coumarin dyes have been incorporated within silica: polydimethylsiloxane Polyceram hosts using the sol-gel process to form crack-free, polishable monoliths. The use of silylated laser dyes allows for covalently bonding the laser dyes to their hosts. Photostability of the samples was evaluated by measuring the decrease in the dye absorption in the Polyceram upon ultraviolet lamp exposure and by monitoring the fluorescence intensity as function of pump pulses from a N2 laser at 337 nm. Both methods showed a significant improvement in photo- and thermal-stability of the silylated dye Polyceram compared to that of the unsilylated dye Polyceram at a dye: Si mole ratio of 10−4:1. The improved stability is attributed to the immobilization and higher degree of caging of the silylated dye Polyceram with respect to the unsilylated dye Polyceram.

Ceramic Films for Optical Applications Code: D7

Recent progress is reviewed on the wet chemical synthesis of films for optical applications. Specific attention is directed to planar waveguides and to electrooptic, non-linear optical and electrochromic films, including recent results obtained in our laboratories.

Molecular engineering and photostability of laser dyes within sol-gel hosts

The use of solid-state dye laser for commercial applications has been limited largely by the poor photostability of the gain medium. Techniques are examined to improve the photostability of Coumarin and Pyrromethene-BF2 567 (PM- 567) laser dyes within xerogel and Polyceram hosts synthesized by sol-gel processing. The photochemical mechanisms by which laser dyes degrade are discussed and determined specifically for PM-567. PM-567 was determined to degrade both by photo-oxidation and acid degradation. Techniques for improving photostability are described from a molecular engineering perspective. These techniques include: covalently attaching the laser dye to the host; controlling the chemical environment of the dye; increasing dye caging by increasing the SiO2 content; removing porosity from the host; and incorporating additives such as hindered amine light stabilizers to minimize photodegradation.

Incorporation of triethoxysilyl functionalized Coumarin 4 in sol-gel hosts

A silylated Coumarin 4 (derCoum) laser dye has been incorporated over a large range of concentrations in sol-gel silica composites. Optically transparent films of derCoum and Coumarin 4 (Coum) doped silica were obtained; and their absorption and fluorescence spectra and fluorescence efficiency were measured. Dye extraction was investigated as a function of sol-gel processing conditions. Dye extraction results indicated that prehydrolysis of the derCoum and full hydrolysis of TMOS resulted in films from which the dye could not be extracted, suggesting that all the dye is bonded within the sol-gel matrix. The silylated dye films showed higher fluorescence efficiency at all concentrations with respect to the normal dye film.

Reversing Gels and Water Soluble Colloids from Aminosiloxanes

The unique sol/gel behavior of an organic/inorganic hybrid material synthesized from 3-aminopropyl-triethoxysilane (3AS) and tetramethoxysilane (TMOS) is discussed and examined. The addition of H2O to a mixture of a basic (3AS) and an acidic (TMOS) alkoxide leads to rapid gel formation. This wet gel reverses to a sol upon heating which is attributed to the dissolution of siloxane bonds between the surfaces of colloidal particles in the gel. The reversed sol dries to an optically transparent solid which is water soluble. The water solubility and the stability of these colloidal particles are described by their aminopropyl/silanol surface and the electrostatic interactions between them using DLVO theory.

Control of porosity in SiO2:PDMS polycerams through variations in sol-gel processing and polymer content

A series of optically transparent SiO2: polydimethylsiloxane (PDMS) polyceram monoliths have been synthesized by two-step acid/base sol-gel processes. Two different processing routes are discussed and compared; one synthetic route (Route 1) utilizes lower water content, shorter reflux times, and faster drying conditions compared to the other synthetic route (Route 2). The Route 1 polycerams were all essentially non-porous at all PDMS contents examined (20 - 80 volume % PDMS). In contrast, the porosity of the Route 2 polycerams varied dramatically as a function of PDMS content. The surface area and pore volume for a 0% PDMS Route 2 polyceram were 573 m2/gm and 0.59 cm3/gm, respectively; the surface area and pore volume decreased with increasing PDMS content. The amount of porosity within the polycerams is proposed to be controlled by the relative rates of condensation and evaporation during processing and by the amount of PDMS trapped in the pores. This idea is supported by the differences in the drying behavior with processing and by the structural information obtained by magic angle spinning solid-state 29Si NMR of the polyceram monoliths. Quantitative evaluation of the 29Si NMR and porosity data are utilized to formulate structural models of these polycerams. The structural models are then specifically used to describe the effect of porosity on the photostabilization of a laser dye doped within these polyceram monoliths.

Optical thin films by wet chemical processing

Wet chemical processing of ceramics, glasses and inorganic-organic hybrids in the form of films has a large number of both proven and potential optical applications. The present review focuses on progress since 1990 in the areas of ferroelectric films, electrochromic and photochromic films, planar waveguides, and NLO films. Where appropriate, advances are illustrated by results obtained in our laboratories.