Oligomeric and polymeric SiPOM materials have been prepared by reacting trichloro endblocked PDMS [degree of polymerization, ∼ 14 (I) and 60 (II)] with α-K8SiW11O39. NMR and IR spectroscopy show that the POM units are bonded to the siloxane via Si-O-W bonds. The reaction of the short PDMS segment (I) with the POM produces powdery materials, (isolated as tetrabutylammonium salts) while the longer PDMS (II) forms elastomeric materials. For the latter the POM anions act as reinforcing fillers. Other important properties of the hybrid materials are their UV absorbency, their electrochromicity, their electrical properties (volume resistivity, ∼1011 ohm-cm; low loss tangent, memory capability) and their film formation.

We report the development and characterization of a new photorefractive multifunctional ormosil consisting of a second-order nonlinear optical chromophore and a charge transporting group covalently bound to a silicon atom. The sol-gel technique is used to process this ormosil into a homogeneous, single-phase material which exhibits electrooptic and charge transporting properties. When doped with a photocharge generation sensitizer, the material shows photorefractivity as evidenced by the electric field dependence of the four-wave mixing diffraction efficiency and that of the two-beam coupling gain.

Organic-inorganic hybrids in which both constituents exhibit electrical dipolar properties have been fabricated. The inorganic constituent was either LiNbO3 or BaTiO3, and the organic constituent was triethoxysilyl 2,4-dinitrophenylaminosilane (TDP) cross-linked with SiO2 Transparent films were made in a 1:1 organic:inorganic ratio. The films were characterized optically. Preliminary indication of interactions between organic and inorganic constituents, particularly in the case of BaTiO3-TDP-SiO2, has been observed.

Vanadium pentoxide/polypyrrole aerogel (ARG) nanocomposites were prepared by hydrolysis of VO(OC3H7)3 using pyrrole/water/acetone mixtures. Monolithic green-black gels with polypyrrole/V ratios ranging from 0.15 to 1.0 resulted from simultaneous polymerization of the pyrrole and vanadium alkoxide precursors. Supercritical drying yielded high surface (150–200 m2/g) aerogels, of sufficient mechanical integrity to allow them to be cut without fracturing. TEM studies of the aerogels show that they are comprised of fibers similar to that of V2O5 ARG's, but with a much shorter chain length. Evidence from IR that the inorganic and organic components strongly interact leads us to propose that this impedes the vanadium condensation process. The result is ARG's that exhibit decreased electronic conductivity with increasing polymer content. Despite the unexpected deleterious effect of the conductive polymer on the bulk conductivity, at low polymer content, the nanocomposite materials show enhanced electrochemical properties for Li insertion compared to the pristine aerogel.

The fluorescence properties of Er3+ in densified sol-gel silica and alkyl-modified silicates are presented. In sol-gel silica, strong infrared (4I13/2→4I15/2) emission was observed over a wide range of Er3+ concentrations. The effect of metal ion co-dopants, which are known to inhibit clustering of Eu3+ in sol-gel silica, on Er3+ fluorescence are also considered. The co-dopants La3+, Y3+, Yb3+, and Al3+ are increasingly more effective at inhibiting Er3+ clustering and promoting a more uniform spatial distribution of Er3+ ions. Lifetime studies were also conducted to assess the extent of hydroxyl quenching.

Organic/inorganic hybrid silica gels are expected to contain a lower amount of water than simple sol-gel silica gels and should be better hosts for rare earth ions. Er3+-doped hybrid organic/inorganic gels were prepared using Si(OC2H5)4 and CH3Si(OC2H5)3, (CH3)2Si(OC2H5)2 or C2H5Si(OC 2H5)3. Er3+ fluorescence spectra and lifetime studies of these gels are presented and compared to simple Er3+-doped sol-gel silica. The effect of organic modification on Er3+ clustering and hydroxyl retention are discussed. Er3+ upconversion properties are also discussed.

The nanocomposite Pt · 62 SiO2 was prepared by sol-gel processing of Pt(acac)2, two equivalents of H2 NCH2 CH2 NH(CH2)3Si(OEt)3 and 60 equivalents of Si(OEt)4, followed by heating of the obtained metal complex-containing gel in air. When the temperature treatment is performed at T ≥ 550°C, elemental Pt is the only crystalline phase. The influence of the calcination conditions (maximum temperature, period of heating) on the size and size distribution of the resulting Pt particles and on the morphology of the SiO2 matrix (surface area, pore volume) was investigated. When the temperature does not exceed 550°C, small Pt particles (3–5 nm) are formed which have a very narrow size distribution. Their size and size distribution are not affected by the period of heating. Gels heated to 550°C still contain about 0.1 – 0.25 wt% carbon. Carbon-free particles are obtained at 950°C However, at temperatures between 750°C and 950°C the average size of the particle increases considerably, and the size distribution gets very broad, particularly for rxtended periods of heating. The specific surface area increases from about 50 m2 /g in the metal complex-containing gel to about 230 m2/g during the oxidation step. At temperatures above 500°C considerable sintering of the matrix occurs. The pore volumes show the same trend. Heating the gels to 500°C results in the formation of nanopores with radii below 2 nm, which disappear again on heating to higher temperatures.

Size and shape of metallic nanoparticles, which are embedded in sol-gel produced glass-like layers, are able to influence the optical properties of coatings on glass. Since the shape of the particles is determined by its crystalline structure, and the structure is modified significantly during the particle growth, the development of both was observed in dependence on the stage of growth applying conventional and high resolution electron microscopy. These investigations carried out on Au and Ag particles have revealed different types of colloidal growth, a real structure often formed by dislocations and twins as well as a relatively high particle mobility.

A process for the synthesis of CdS nanoparticles embedded in hybrid organic/inorganic silica matrices has been developed, based both on colloid and sol-gel chemistry. The large possibilities offered by these techniques allow the study of the influence of various parameters on the luminescence properties of the nanoparticles. Two directions were investigated: first, we characterized the surface of the nanoparticles complexed with an organic thiol using NMR spectroscopy. Then, we synthesized new systems to study the influence of chemical modifications, such as the composition of the aggregates (CdS:Mn), the surface (CdS/ZnS core/shell nanostructures) and the interface between the aggregate and the gel matrix.

The alkoxides M(ORX)n wherein M is an alkaline-earth or rare-earth and ORX is a fluoroalkoxo or bromoalkoxo group exhibit the properties to form pure fluoride materials by hydrolysis at room temperature. Using this property, we synthesized pure barium and europium fluoride and pure alkaline-earth bromide. The hydrolysis of an heteroleptic species, Ba(OCH2CH2Br)[OCH(CF3)2] allowed pure and crystalline BaFBr materials to be obtained at room temperature.

To design new second order nonlinear crystals, we have haracterized a series of dipeptide complexes and copper glutamate. We tested 16 materials using powder second harmonic generation. The best of these materials was copper glutamate. Results of initial nonlinear optical characterization of the copper glutamate powder determined by the Kurtz powder test are presented.

Second order nonlinear optical properties (NLO) require the presence of a polarizable moiety situated in an anharmonic potential. Our approach to incorporating such properties into self-assembled multilayers involves use of asymmetric α,ω bisphosphonates which meet this requirement by virtue of their chemical structure and binding properties. We have developed and optimized protection and deprotection schemes to allow for oriented layering of these molecules. Characterization by optical ellipsometry and grazing angle X-ray diffraction provides insight on average layer thicknesses and bulk film densities. Second harmonic generation (SHG) intensity from the bulk film is measured to verify NLO activity.

A novel sol-gel technique was used to immobilize malachite green ions (MG+) in stable, optically transparent, porous silica gel films. A simple and sensitive method was developed for the detection of cyanides in solutions using spectrophotometry to measure changes caused by cyanide ions (CN−) in the absorption spectra of the green-colored silica gel films. After reaction with cyanide ions, the absorption spectra of the films changed with a typical decrease in absorbance at 620 nm. On the basis of the absorption spectra of the films, a portable and easy to use fiber optic cyanide film sensor was fabricated. Decolorization undergone by the greencolored gel films, as they were exposed to cyanide ions, was detected through a fiber. Preliminary results indicate concentrations on the order of a few ppm are detected using the fiber optic sensor.