Tetrakis(4-carboxyphenyl)porphine (TCPP), which is well known as a photochemical hole burning (PHB) dye, was incorporated in amorphous silica materials (a-SiO₂) by a sol-gel process with using tetramethoxysilane (TMOS) and aminopropyltriethoxysilane (APTES). With using APTES as precursor of silica gel, TCPP was cross-linked to a-SiO₂ matrix through aminopropyl group of APTES. The cross-linkage of TCPP and APTES was confirmed by the FT-IR measurement. The TCPP incorporated in a-SiO₂ matrices showed activity in PHB. In the TCPP cross-linked a-SiO₂, properties of photochemical hole, such as hole width, quantum efficiency and irreversible broadening under cycle annealing experiment, were improved. A burnt hole at 3.6 K was observed after cycle annealing experiment up to 80 K in the TCPP cross-linked a- SiO₂.

Several dyes such as a spiropyran, a spirooxazine and two tetraarylporphyrins have been incorporated inside hybrid organic-inorganic matrices synthesized through the acid hydrolysis of dimethyldiethoxysilane and zirconium n- propoxide. These matrices are nanocomposites with well defined hydrophilic (zirconium oxopolymer nodules) and hydrophobic (polydimethylsiloxane chains) domains. As a consequence, they are good candidates to investigate dye-matrix interactions in matrices containing transition metal. These interactions are shown to occur through hydrogen bonds, covalent bonds or Lewis acid-base type bonds. They strongly modify the optical response of the dyes (absorption-emission spectra, lifetime, kinetics...).

One of the simpler organic/inorganic hybrids to prepare by the sol-gel process is polyethylene (PEO)/silica. The reason for its simplicity is that PEO is soluble in water. PEO contains ether oxygens -(O-CH₂-CH₂-)- that readily form hydrogen bonds. The refractive index of PEO is low, 1.4537, and its glass transition temperature can be as low as minus 65 degrees Celsius, generally making it a crystalline polymer at room temperature. Hybrids of PEO/silica were prepared with molecular weights 200, 1000, 2000, and 3400. The lower molecular weights (200 and 1000) produced transparent hybrids over a range of loadings. The higher molecular weights (greater than 2000) produced samples that were sensitive to the loading and especially the time of mixing before the samples were cast into closed containers. These trends indicate a competition between the reactions that lead to gelling and the tendency to phase separate. By following these trends, both the scale of the microstructure and the degree of transparency was adjusted.

The preparation of organic-inorganic hybrids based on the use of sol-gel chemistry offers a creative approach for synthesizing novel optical materials. Specifically, hybrid materials derived from combining silica and acrylic systems have been shown to be effective host matrices for organic laser dyes. However, the synthesis must be carefully designed in order to retain the beneficial properties of both constituents within a single hybrid network, without compromising optical quality. In this paper, three approaches for initiating polymerization reactions of the organic component are reported. Raman and optical spectroscopies are used to correlate the influence of organic and inorganic network development on optical transparency of the hybrid. The most successful synthesis method involved dissolving the sol components in a common solvent before instituting polymerization treatments. Materials synthesized from this approach satisfy three important criteria for organic- inorganic hybrid layer host materials: an optically transparent matrix with little or no phase separation; equal amounts of organic and inorganic to obtain the benefits of both phases; and a high degree of organic polymerization.

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.

In this paper, we describe up-converted luminescence and reverse saturation absorption of metalloporphyrins of CuTPPS and ZnTPPS in aluminosilicate sol-gel materials. The photo- upconversion luminescence is believed to arise from the radiative recombination of the second excited singlet (singdoublet) state. These effects are attributed to the higher excited state absorption. The dynamic analysis for the excited state processes indicates that the saturation or reverse saturation absorption is dependent on the ratio of the average absorption cross-section of the excited states to that of the ground state. The absorption cross-sections of the excited states are estimated.

In this work, new hybrid organic-inorganic composites of C₆₀-NH₂(CH₂)₃Si(OC₂H₅)₃ (C₆₀-3- Aminopropyl-triethoxy-silane, C₆₀-KH550), C₆₀-NH₂(CH₂)₃Si(OC₂H₅)₃-CH₂OCHCH₂O(CH₂)₃Si(OCH₃)₃ (C₆₀-3-Aminopropyl- triethoxy-silane-3-Glcidoxypropltrimethoxysilane,C₆₀- KH550-KH560), and C₆₀-NH₂(CH₂)₃Si(OC₂H₅)₃CH₂OCHCH₂-O-(CH₂)₃-Si(OCH₃)₃- (CH₃)₂Si(OCH₃)₂ (C₆₀-3- Aminopropyltriethoxysilane-3-Glcidoxypropltrimethoxy-silaneDi- ethoxy-dimethyl-silane, C₆₀-KH550-KH560-DTDS) were synthesized with sol-gel processes. The infrared absorption spectra of the composites were measured. Using a Nd:YAG laser with 10 ns pulse duration and 532 nm wavelength, the optical limiting behaviors of the above composites were demonstrated and discussed. As optical limiters, the laser induced damage thresholds of the slices made from such hybrid materials can be up to 5-6 J/cm².

Hemicyanine doped silica film was fabricated by sol-gel technique. Time evolution of structural changes in hemicyanine and their influence on the second order optical nonlinearity were investigated through UV-Vis absorption and the second harmonic generation measurements. Three factors were found to have dominant influence on the self alignment and optical nonlinearity of the film. Self alignment was believed to complete right after the evaporation of the solvent. Conversion of protonated hemicyanine to monomeric hemicyanine occurred within 4 hours after film deposition. During this period of time the SHG signal continued to rise and finally reached the maximum. The growth of optical nonlinearity was mainly due to deprotonation of hemicyanine molecules. Optical nonlinearity of the film can also be increased by reducing the amount of hemicyanine aggregates in the film. Blue shift of the absorption peaks for aggregate was found during the drying of the film, it was attributed to resulted from enhanced molecular interaction.

Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for spherical cavity structure. Hydrolysis and polymerization processes of phenyltriethoxysilane (PTES) as a starting material was pursued by observing the change of PTES/R6G in HCl solution with its optical absorption and viscosity. As the polymerization of PTES proceeded, increase of molecular size resulted in change its properties from hydrophilic to hydrophobic, and subsequently the solution separated into two layers of aqueous and organic. Polymerized PTES in the organic layer showed good affinity with incorporated R6G, and high monomer/dimer ratio in particles was achieved. Moreover, using them intermixing of unsuitable particles of submicron size was avoided, because hydrolyzed PTES of small molecular size that is the origin of submicron-sized particles was removed to the aqueous layer. With stirring, titration of diluted droplets containing polymerized PTES was suitable for preparing several micrometer sized particles, and followed by solidification in ammonia water. Degree of the polymerization of PTES and viscosity of liquid droplets were the key factors for determining the properties of R6G-doped spherical particles of optical cavity structure.

Within the large list of organically doped sol-gel materials with optical or electro-optical applications, two representative examples shall be presented: first, gel-glass dispersed liquid crystal (GDLC) devices with electro-optical properties related to an adequate sol-gel chemical processing for trapping microdroplets of nematogenic organic compounds (i.e. liquid crystals, LCs), and second, photochromic-doped sol-gel materials attached to optical fibers, for which, the properties of the light throughput and the response time may be modified by the device features.

Two novel holographic recording media based on silica gel methyl methacrylate (MMA) and hydroxy ethyl methacrylate (HEMA) organically modified ceramics (ORMOCERS) are presented and its holographic properties, inferred from the experimental data, are discussed. The recording of holographic gratings of both low-spatial frequency (50 lp/mm) and high-spatial frequency (1400 lp/mm) in a bulk ORMOCER matrix is reported. The gratings were recorded by UV irradiation-induced photopolymerization of the MMA or HEMA monomers embedded in the silica matrix. The Bragg gratings were successfully recorded by interference of two coherent beams of 351.1 nm wavelength. A linearly polarized He-Ne laser beam (632.8 nm) was used for continuous monitoring of the recording process by measurement of the diffraction efficiency and for enhancement of the grating creation process. High diffraction efficiencies (93%) and low absorption and scattering coefficients were measured during the holographic reconstruction by He-Ne laser beam. The most important holographic parameters of the gratings were inferred from the experimental data: diffraction efficiency, angular selectivity, refraction-index modulation amplitude, spectral sensitivity, the Klein-Cook parameter, and the environmental stability of the gratings.

Laser oscillation was easily achieved in all hand polished rhodamine 6G, DCM and rhodamine 6G + DCM doped titania containing ormosil xerogels. Two kinds of xerogels prepared by sol-gel method were used as dye hosts. Their optical properties and microstructural characteristics were reported. Slope efficiency, photostability, tunable bandwidth and surface damage threshold of these dye lasers were examined. The effect of dye concentration and dye-matrix combination on the fluorescent emission, slope efficiency, photostability and tunable bandwidth was discussed. Laser efficiency of 13% and photostability of 5400 pulses at 4 J/cm², 1 Hz repetition was obtained in 2 X 10^-4 rhodamine 6G doped dye laser.

The construction and the operation properties of an organically doped, sol-gel cladded optical fiber pH sensor, are described. The silica-entrapped indicator in the fluorescence-based device was fluorescein, pumped with a continuous wave (cw) argon 488 nm laser. The transmitted signal through the sensing fiber yielded a response in the pH range of 4 - 7, where signal level increased from acid to base. The device is durable and renewable. When tested over more than 8 weeks it retained its response, as demonstrated by dozens of cycles of measurements each lasting a few hours. The probe is easily prepared under regular room conditions by simple decladding of the fiber and sol-gel recoating. System design and setup are attractive due to modularity and discardable low cost probe tips.

A novel material is described for holographic light shaping diffusers based upon monolithic glass fabrication that is totally optically refractive. This diffuser has mechanical and optical properties far superior to plastic diffusers, making it suitable for use in optical systems that include high power lasers, ultraviolet applications, near infrared applications, and for high-temperature environments. We have designed and implemented an all glass diffuser. This novel diffuser is a monolithic optical element that controls the angular spread of transmitted light and homogenizes otherwise spatially noisy light sources such as LEDs and filamented light sources while maintaining damage thresholds consistent with any glass optical element. Preliminary analysis shows that this glass diffuser has a transmission efficiency of 90% from the ultraviolet wavelengths through the visible spectrum and into the near infrared.

Structural formation of dip-coated silica sol-gel thin films is monitored in situ via fluorescence depolarization with luminescent probe molecules. Pyranine (trisodium 8-hydroxy- 1,2,6-pyrenetrisulfonate) and prodan [6-propionyl-2- (dimethylamino)naphthalene] are chosen as the probe molecules for these experiments and are dissolved into the sol gel solution in millimolar quantities. This provides sufficient luminescence intensity without interfering with the film drying process. Fluorescence depolarization yields results which directly correlate to microviscosity increases as the film progresses from liquid to solid. These results allow for further quantitative support of a model previously presented concerning the formation of sol-gel thin films.

Two types of sol-gel derived redox modified electrodes are introduced. Anthraquinone modified silicate films were produced from 1,5-di-[(3- trimethoxysilyl)propylamino)anthraquinone derived sol by dip- coating of ITO coated microscope slides. The monomer was synthesized from commercially available 3- aminopopyltrimethoxysilane and 1,5-dichloroanthraquinone. Prussian blue modified electrodes were produced by cycling the potential of a preformed, porous Fe²⁺ doped silicate film coated on ITO substrate in a potassium ferricyanide solution. In both cases, cyclic voltammetry and electronic spectra of the films show that more than 100 layers of redox monomers are electrochemically active, which indicates long range charge transport by electron self exchange mechanism.

Relatively new modification methods for densification of sol- gel derived silica films using electronic excitations and water vapor were investigated. Dried silica gel films were found to be densified by vacuum ultraviolet irradiation and He⁺ ion implantation. The densification is deduced to be ascribed to dehydration and cleavage of the strained bonds through electronic excitations induced by the irradiations. The structure of the irradiated silica films is similar to that of silica glass densified under a high pressure. The exposure to water vapor at 80 degrees - 180 degrees Celsius is also effective in densification and dehydration of sol-gel silica films. These methods are expected to be valuable for fabrication of dense silica films at low temperatures. However, the silica films densified by the irradiations and the exposure are suggested to contain a strained network because a subsequent annealing above 300 degrees Celsius induced structural changes through a thermal relaxation.

The formation of a borosilicate glass film of 10 - 20 micrometers in thickness on a silicon substrate via an interfacial polymerization technique has been studied as the first step for the preparation of a planer waveguide for optical communication. A gel film prepared from the partially hydrolyzed TMOS mixed with boron alkoxides could be densified into a glass film of 16 micrometer in thickness having a smooth surface by the heat treatment up to 1000 degrees Celsius. A good reproducibility in the yield was obtained by completing the hydrolysis and condensation of the whole ingredient in the 5 ml of precursor solution spread over water containing triethylamine as a catalyst within a cylindrical container of about 80 mm inside diameter. The use of saturated aqueous solution of boric acid instead of distilled water was necessary to hinder the re-dissolution of boron from the formed gel film.

New organic-inorganic fluorescent thin gel films included with laser dyes or fluorescent organic pigments have been prepared for display application. The florescent dyes (benzoxazolium, pyrromethene, and rhodamine dyes) and super-fine particles of fluorescent pigments (coumarin and perylene) were successfully incorporated into thin silicate gel films prepared from tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and methoxysilane oligomer (MTSO) under acid catalyzed hydrolysis. The blue, green, and red luminescence were observed from these thin films (thickness: 100 - 400 nm), respectively. Fluorescence spectra, fluorescent quantum yield and lifetime of thin gel films are examined. Fluorescent peaks for most of dyes and pigments used in gel films were similar to those in solution, and fluorescent lifetime for dyes and pigments used in gel films were 2.9 - 4.5 ns. Photostability of fluorescent gel films is dependent on fluorescent organic dyes and pigments used and/or silicate gel matrixes. Coumarin and perylene pigments have higher fluorescent quantum yield in gel film prepared from MTSO. The large Stokes shift was observed in fluorescent gel film using coumarin and benzoxazolium dyes. The coumarin and perylene pigments are significantly photo- stable in gel film prepared from MTSO, and photodegradation of perylene red after irradiation of 500 W Xi-lamp for 30 min is below 20%.

Alumina thin films with a roughness of 20 to 50 nm were formed by immersing the porous alumina gel films prepared by the sol- gel method in boiling water. When hydrolyzed fluoroalkyltrimethoxysilane was coated on the alumina films, the films showed super-water-repellency and high transparency; the contact angle for water of the film was 165 degrees and the transmittance for visible light was higher than 92%. When the fluoroalkyltrimethoxysilane-coated thin films were heat- treated at temperatures higher than 500 degrees Celsius, the films became super-hydrophilic; the contact angle for water on the films was less than 5 degrees. It was shown the existence of air in the pores on the surface caused the super-water- repellency and that of water in the pores caused the super- hydrophilic property. The transparent, super water-repellent and super-hydrophilic coating films formed on glasses, metals, and ceramics have practical applications such as optical lenses, eye-glasses, cover glasses for solar cells, windshields of automobiles, and so on.

Photosensitivity of Al₂O₃ and Al₂O₃-SiO₂ gel films, which were derived from Al(O-sec-Bu)₃ modified with a variety of (beta) -diketones was studied. These gel films exhibited optical absorption bands in a UV-range, associated with the (pi) -(pi) * transition in the chelate rings of the (beta) -diketonato ligand. The irradiation of the gel films with UV-light corresponding to this transition decreased the solubility of these gel films in organic solvents or acidic aqueous solutions, accompanied with the dissociation of the chelate rings. Based on the change in solubility by the UV-irradiation, fine-patterns of Al₂O₃ and Al₂O₃-SiO₂ thin films, containing over 30 mol% Al₂O₃, were formed on various substrates. The incorporation of benzophenone in Al₂O₃ gel films was also found to improve their photosensitivity. Moreover, it was demonstrated that the present photosensitive gel films were applicable to the fabrication of diffraction gratings using excimer laser and a phase mask.

A comprehensive study of the luminescence quenching behavior of ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline perchlorate dissolved in various sol-gel matrices was performed. Thin films of submicron thickness were formed by depositing tetraethyl orthosilicate (TEOS) gel solutions, organically modified with methyltrimethoxysilane (MTMS), onto glass slides using conventional spin-coating methods. Systematic changes in composition were conducted to examine the structural properties of the sol-gel silicate thin films for possible use in fluorescence sensing applications. Luminescence quenching in the presence of oxygen was analyzed as a function of varying sol-gel composition. Modeling techniques were employed to determine the best exponential decay curve fit of different thin film samples. The degree of luminescence quenching was found to be greatest in the polar TEOS thin films. However, whereas cracking was prevalent in the pure TEOS thin films, certain levels of organic modification with non-polar MTMS prevented cracking while maintaining a high degree of fluorescence quenching. These organically modified sol-gel thin films appear to be the most suitable for fluorescence-based oxygen sensing applications.

LiTaO₃ thin films were deposited on platinized silicon and silicon wafers by spin coating. Double alkoxides, dissolved in parent alcohols were used as the sol precursors. Five different organic ligands, R equals CH₃, C₂H₅, n- C₃H₇, i-C₃H₇, and n-C₄H₉ were selected to study their effect on preferred orientation in the crystallized phases of the sintered films, which were analyzed by the x-ray diffraction techniques. It was found that the different ligand types gave rise to changes in direction as well as degree of the preferred orientation. The influence of the ligands also varied with the film thickness. As the thickness of the films increased to greater than 200 nm, only the double ethoxide derived films on platinized Si can maintain good degree of preferred orientation at the [110] direction. Possible causes for these effects are discussed. As an example for its applications, a thin film device utilizing the pyroelectric properties of LiTaO₃ are briefly described.

Cyanine dye which is now widely used as recording media in write-once optical disks was doped into ormosil precursor solution via sol-gel method. The dye-doped ormosil films were prepared by spin coating process. Optical recording experiment was performed on the sol-gel films. More than 45 dB of carrier to noise ratio was obtained in the sol-gel films under normal writing/reading conditions of recordable-CD. This shows the ability of the ormosil as the host of the dye for optical disks.

Single layer quarterwave antireflective (AR) coatings are widely used on many of the transmissive optics in high power fusion lasers. With these coatings maximum efficiency is only obtained at one wavelength. In those applications involving harmonic converter crystals, however, broader band performance would be advantageous because light of two wavelengths is involved. A simple two layer broadband coating has been developed which consists of a layer of a methyl silicone polymer overcoated with porous silica. This is prepared from methyltriethoxysilane and tetraethyl silicate, respectively. Both reagents are distilled to the highest purity so that the coatings are non-absorptive and have the highest laser damage threshold. Less than 0.5% reflection over a broad wavelength range can be obtained on substrates in the 1.46 to 1.51 index range.

The fabrication of nanoparticles by the sol-gel process and their use in polymeric or sol-gel-derived inorganic-organic composite matrices opens up interesting possibilities for designing new optical materials. Two different routes have been chosen for preparing optical nanocomposites: The first is the so-called 'in situ route,' where the nanoparticles are synthesized in a liquid mixture from Zr-alkoxides in a polymerizable system and diffractive gratings were produced by embossing uncured film. The second is the 'separate' preparation route, where a sterically stabilized dry nanoboehmite powder was completely redispersed in an epoxy group-containing matrix and hard coatings with optical quality on polycarbonate were prepared.

A radial gradient-index (r-GRIN) material with low distributed dispersion (T₁₀ equals 0.003, V₁₀ equals 340) was successfully prepared by sol-gel process in SiO₂-TiO₂BaO-K₂O system. The r-GRIN lens with flat surfaces performed little chromatic aberration. Sol-gel synthesis process using metal salts to realize the r-GRIN materials with low distributed dispersion was investigated. The low distributed dispersion was achieved by convex distribution for barium and even distribution for titanium against silicon along a diameter. The sol-gel process enables to prepare r- GRIN materials which have necessary low distributed dispersion on demand.

Sm²⁺-doped glasses in the system of Al₂O₃-SiO₂ were prepared by the sol-gel processing of metal alkoxides and the reaction with H₂ gas at 800 degrees Celsius, of which hole burning properties were investigated. Sm³⁺ ions-containing glasses prepared by a sol-gel method were reacted with H₂ gas to form the Sm²⁺ ions. Fluorescence line narrowing spectra of the ⁵D₀ yields ⁷F₁ transition were analyzed to study the local structure surrounding the Sm²⁺ ion. It is concluded that the Sm²⁺ ions are closely coordinated with nine oxygens of the AlO₆ group in aluminosilicate glasses and the addition of Al³⁺ ions into glass induces an increase in the coordination number of the Sm²⁺. The fluorescence intensity of the Sm²⁺ and Sm³⁺ ions considerably increases in glasses containing more than 5 mol% Al₂O₃. The holes were burned in the ⁷F₀ yields ⁵D₀ line of the Sm²⁺ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to approximately 15% of the total intensity within a few hundred seconds. The hole width was 3 cm^-1 full width at half maximum at 77 K and increased with increasing temperature.

The sol-gel method is convenient for preparing amorphous transparent oxides with a wide range of optical properties including laser action, optical gain, phosphorescence, SHG and other non-linear effects. The sol-gel method was used to produce sol-gel samples using metallophthalocyanines. From metallophthalocyanines we used Cu (II) phthalocyanine (beta) - form, Ni (II) phthalocyaninetetrasulfonic acid, tetrasodium salt, Cu (II) 3,10,17,24-tetra-tert-butyl-1,8,15,22-tetrakis (dimethylamino)-29H, 31H-phthalocyanine, Zn 1,4,8,11,15,18,22,25-octabutoxy- 29H,31H-phthalocyanine Ni (II) 5,9,14,18,23,27,32,36-octabutoxy- 2,3-napthalocyanine and Cu (II) 5,9,14,18,23,27,32,36-octabutoxy-2,3-napthalocyanine. In our paper we report and discuss the results obtained from the measurements of the index of refraction using the prism coupling technique, absorption spectra and non-linear transmission measurements using picosecond laser pulses. The absorption spectras of Cu, Zn and Ni phthalocyanines in solution and sol-gel matrix showed decomposition. We found optical limiting after 0.2 J/cm² in Ni (II) phthalocyaninetetrasulfonic acid, tetrasodium salt solution; glass samples showed no optical limiting. The mean of the index of refraction measured for all the (beta) -Cu phthalocyanine samples was 1.42. No birefringency was found.

A new laser processing technique was proposed and demonstrated for producing high-temperature sol-gel coatings on substrates like ZnSe or chalcogenide infrared fibers which cannot be exposed to relatively high temperatures involved in most sol- gel processes. Our approach is similar to the 'indirect writing' technique except that an air gap is inserted between the sol-gel coating and the light absorber so as not to affect the optical coating. Our processing technique integrates optical sol-gel coatings having tailored properties of porosity, surface area, and surface affinity with substrate materials used for integrated and fiber optic infrared technologies such as optical sensors.

A physically and chemically benign method for patterning multiple sol-gel materials onto a single substrate is described. Structures are demonstrated for potential micro- optical chemical sensor, biosensor, and waveguiding applications. Fabrication is based on the micro molding in capillaries (MIMIC) approach. A novel mold design allows several sols to be cast simultaneously. Closely spaced, organically modified silica ridges containing fluorescent dyes are demonstrated. Ridges have cross sectional dimensions from one to 50 micrometers and are centimeters in length. Processing issues, particularly those related to mold filling, are discussed in detail. Because sol-gel MIMIC avoids the harsh physical and chemical environments normally associated with patterning, the approach allows full exploitation of sol- gel processing advantages, such as the ability to entrap sensitive organic dopant molecules in the sol-gel matrix.

Sol-gel technology has been used to fabricate fiber optic and integrated optic chemical sensors for environmental monitoring and process control applications. These multi-sensing element sensors offer many advantages, the most prominent being that they are miniaturized, lightweight, and immune to electromagnetic interference. We are developing versatile, multi-analyte, micro-miniaturized fiber optic chemical sensor (FOCS) and integrated optic chemical sensor (IOCS) technologies for use in closed-loop control and process monitoring for industrial and environmental applications.

Conventional sol-gels are rather hydrophilic. A more hydrophobic material is obtained by preparing organically modified siloxanes (ormosils). We have used three different solvatochromic dyes, (1) ET-33, the best solvatochromic probe known so far, (2) Nile red (NR), and (3) a ketocyanine (KC) dye, all with unique solvatochromic properties in both absorption and fluorescence, to probe the micro-polarity of sol-gels. Because ET-33 has a very low molar absorbance and is not fluorescent at all, and KC was hardly soluble in the sol- gel solution, NR was preferably used. NR is an excellent probe and sensitive to the polarity of its microenvironment. Spectroscopic studies reveal remarkable changes in the absorption band positions as a function of the polarity of the sol-gel which depends on the different precursors used. Furthermore, aging time and temporal stability as a function of different ormosils have been investigated.

Sol-gel SiO₂ - TiO₂ multilayers (containing 20 mol% TiO₂) have been deposited by spin-coating onto single crystal Si substrates previously covered with a SiO₂ buffer layer (approximately 4 micrometers), also prepared by sol-gel. The silica-titania films were first densified at 900 degrees Celsius and were then subjected to selected crystallization heat treatments at 1000 degrees Celsius, in order to precipitate different volume fractions of anatase (TiO₂) crystallites, between 2.5 and 15%. The optical loss of these nanocomposites was measured at different wavelengths, using argon ion and He-Ne laser light. The experimental loss values, after removing the intrinsic Rayleigh term and surface scattering, were compared to scattering losses calculated by means of the Rayleigh-Mie theory, for light scattering by spherical particles, which was used to examine the influence of different parameters: radiation wavelength, nanocrystallite size and volume fraction of nanocrystals. The theoretical calculations show that, for the wavelengths of interest ((lambda) on the order of or greater than 1 magnitude), nanocrystallite scattering losses remain below 0.5 dB/cm, even for volume fractions as high as 15%, as long as their diameter is below 11 nm. The experimental results agree reasonably well with the theoretical predictions, considering the approximations made. The extension of the model to the study of residual film porosity led to the conclusion that typical porosity present has a negligible influence on the total waveguide loss.

Surface plasma resonance (SPR) of metal nanoparticles embedded in dielectric media was briefly reviewed on the basis of electromagnetic theory, where how SPR can enhance the oscillating field of light was illustrated. It was stressed that any photoexcitation processes can be enhanced by SPR as long as they occur at SPR wavelength, and this serves a basis for innovative SPR-assisted optical functions. In order to utilize SPR for enhancing a photoexcitation process of interest, SPR characteristics such as wavelengths should be controlled. Sol-gel method was shown to have great advantages in controlling SPR characteristics through controlling the metal particle size, shape and orientation and selecting the surrounding media. A recent attempt to develop materials of SPR-assisted photoelectrochemical functions was also described.

Glassy composite materials containing oriented magnetic fine particles are expected to have large residual magnetization and coercive force because of their fine magnetic domain structure, and also to show magnetic and optical anisotropy which result from their oriented dispersive condition. The silica (SiO₂) gels and glassy materials containing oriented magnetite (Fe₃O₄) fine particles were prepared by sol-gel method. The magnetic anisotropy of the samples were investigated by ferromagnetic resonance (FMR) spectra. The samples had uniaxial magnetic anisotropy that was evaluated from the angle dependence of FMR spectra. The coercive force of the glassy material was much larger than that of the gel because of the stress induced by the densification of the gel. Magneto-optical property of the samples was evaluated by the measurement of Faraday rotation angle in visible light region under no external magnetic field. The gel showed positive Faraday rotation with maximum at around 470 nm, however, the wavelength of maximum shifted to 700 - 800 nm in glassy sample. The Faraday rotation of both gels and glassy materials with no magnetic field was induced by the residual magnetization of the magnetite fine particles, and the change of magneto-optical spectra after densification also suggests the magnetite fine particles were subjected to the stress in the glassy materials.

Semiconductor CdS quantum dot-doped sodium borosilicate glasses were successfully fabricated by the sol-gel technique. The dot size and concentration of CdS are controlled by chemistry and processing conditions. Optical absorption spectra were measured for these quantum dot-doped glasses, and absorption shoulder due to the exciton effect was observed. Nonlinear optical properties of high third-order susceptibility, (chi) ⁽³), and room-temperature optical gain were observed. Potassium ion exchange was performed on the glass, and channel waveguides were successfully fabricated in the CdS-doped glass. The waveguide was tested with single mode laser pulses, and single mode output was demonstrated. Spectral broadening of the output pulses was observed.

CdTe quantum dot (QD)-doped sodium borosilicate (NBS) glasses with particle sizes ranging from 2.4 nm to 8.5 nm were synthesized by the sol-gel technique. Two sol-gel methods were developed. Method (1) involves the immersion of CdO-doped gels in Na₂Te/methanol (MeOH) solution for 1 to 4 days at 60 degrees Celsius, followed by heat-treatment at 540 degree Celsius or 570 degrees Celsius for 6 to 12 hours in an inert atmosphere. In method 2, CdTe QDs were directly formed at various temperatures (520 degrees Celsius to 570 degrees Celsius) under a reducing atmosphere. The synthesis of CdTe QDs in the NBS glass was accomplished using cadmium nitrate [Cd(NO₃)₂] and telluric acid (H₆TeO₆) as the starting materials. The number density and particle size distribution of the CdTe nanocrystallites depend on the heat- treatment conditions for the reduction of Te⁶⁺ to Te^2- ions and their subsequent ions react with Cd²⁺ ions to form CdTe. The absorption edges of these glasses were blue-shifted due to quantum confinement depending on the concentration of the initial salt and the heat- treatment conditions.

Nano-sized, phenyl-capped CdSe quantum dots were isolated, after preparation inside reversed micelles present in AOT/H₂O/heptane, and then successfully redispersed in the amino- silicate ormosil (i.e. organically modified silicate) derived from 3-aminopropyl-(trimethoxy)silane. Doped ormosils were formed into films of a few micrometer thickness or small bulk samples. The ormosils were structurally characterized by means of absorption spectroscopy in the visible and near-infrared ranges, and by ²⁹Si solid state nuclear magnetic resonance spectroscopy. The siloxane matrix of the amino-silicate ormosil was found to be 84% condensed and polymeric water molecules are hydrogen bonded into the matrix, presumably at silanol and amine sites. CdSe dots of apparently good monodispersity and radius 1.5 to 2.4 nm (going from yellow to red in visual appearance) were redispersed in the amino- silicate ormosil. Attempts to prepare larger dots resulted in flocculation of the CdSe. The maximum loading of CdSe dots in the amino-silicate matrix was measured to be 2.05 weight% CdSe_0.72, where the density of the amino-silicate host was around 0.5 to 0.7 of the density of a typical, melt-derived silicate glass.

We present two approaches for the sol-gel synthesis of transparent solids in which CdS nanoparticles are homogeneously dispersed. In any case CdS nanocrystals are obtained by precipitation either in reverse micelles or in the presence of a complexing thiol. The grafting of the 4- fluorothiophenol at the surface of the particles leads to highly concentrated colloids in acetone. In a first approach, CdS/silica nanocomposites are prepared introducing this concentrated CdS colloid in a silica sol which contains 3- mercaptopropyltrimethoxysilane to ensure the homogeneity of the CdS dispersion. The luminescence properties of the materials are improved by using methyltriethoxysilane instead of tetraethoxysilane as the alkoxide precursor of the silica matrix. Further increase of the luminescence efficiency is also observed if a single Mn2+ ion is present inside the CdS particle. In a second approach, pure CdS nanocrystalline materials (bulk or thin films) are obtained from the sol-gel processing of the concentrated colloids stabilized by 4- fluorothiophenol. The mechanisms driving the aggregation of the particles and the gelation of the system are explicited. Thin films as well as monoliths can be produced. The general principles of this method are not restricted to chalcogenide materials, and should therefore enlarge the applications of the sol-gel proces to other non-oxide materials.

Gas phase silicon alkoxides react with the wet surface of mammalian cells, affording a stable and homogeneous layer of amorphous SiO₂ modified by Si-CH₃ and Si-H bonds. Layer thickness may be controlled by exposure time. The layer does not suppress cell viability or functionality, and may be applied to cells supported on a trapping network or to cell aggregates. H4-II-E-C3 rat hepatoma cells, Hep G2 human cancer cells and human fibroblasts on various supports were encapsulated by the SiO₂ layer and studied in terms of glucose utilization and ³H-leucin incorporation into secreted proteins. In the case of pancreatic islets, encapsulation was carried out without supports, so that original islet volume and features were maintained. In vitro results indicate preservation of vitality and function, as tested by insulin production.

An autostoichiometric vapor gel deposition approach is demonstrated for ferroelectric LiTaO₃ and LiNbO₃ thin films. This approach utilizes the partial hydrolysis of hygroscopic alkoxide in the vapor phase, and the subsequent polycondensation on a heated substrate. Epitaxial films with precisely controlled stoichiometry were obtained. Ultra low temperature deposition was achieved taking advantage of the inherently low temperature sol-gel chemistry. The vapor phase hydrolysis of alkoxides provided a mild deposition reaction that allows for the autostoichiometric deposition. The vapor gel method appears to possess the combined advantages of sol- gel processing and MOCVD.

A wide range of ferroelectric and pyroelectric films have been synthesized using wet chemical processing techniques. With appropriate selection of composition and precursors, and with appropriate use of processing methods to develop desired microstructures, films with exceptional combinations of properties have been prepared. The present paper provides an overview of recent results obtained in our laboratories on ferroelectric and ZnO films, and on the integration of such films into device structures. Specific discussion is directed to the effects of chemistry and important processing variables on the structure and properties of the resulting films. Also discussed are the important aspects of device structures utilizing such films.

This study of the sol-gel growth of ferroelectric particles in glass is divided into two sections: The first part deals with the growth of fine crystals of BaTiO₃ and LINbO₃ in SiO₂ glass, the second is concerned with the materials resulting from the modification of the oxide matrix with a silsesquioxane precursor RSiO_1.5, in which R is the optically active organic dinitrophenyltrimethoxysilane, a derivative of aniline. For temperatures as low as 200 degrees Celsius, small semi-crystalline structures have been observed via TEM; they grow in size and concentration with time and heat treatment temperature. P-E loops have been observed in the materials. The organically modified lithium niobium and barium titanium siloxanes also exhibit P-E loops. An interaction between TDP and the barium-titanium metal alkoxides has been observed through a strong red shift in the absorption spectrum of the TDP. This interaction was not observed in the case of lithium-niobium precursors.

Single and multilayer sol-gel coatings of transparent antimony-doped tin oxide (SnO₂:Sb) have been prepared on borosilicate and fused silica substrates using either a 5 mole% SbCl₃ doped 0.5 M solution of SnCl₂(OAc)₂ in ethanol or a water suspension of crystalline Sb-doped tin oxide nanoparticles. The nanoscale morphology and the electrical parameters of the layers have been determined after different firing procedures and heating rates varying from 0.2 to 4300 K/s obtained either in a furnace or by cw carbon- dioxide laser irradiation. For a given sintering temperature (approximately 540 degrees Celsius) a slow heating process in furnace leads to porous, homogeneous single and multilayers consisting of small crystallites. They present a high resistivity of about (rho) equals 4 multiplied by 10^-2 (Omega) cm. With increasing heating rate the layers become denser with larger crystallites and the resistivity value decrease down to approximately 7 X 10^-3 (Omega) cm for 4300 K/s (carbon-dioxide laser sintering). It is proposed that the densification of the coatings is determined by a competition between nucleation at low temperatures and the growth of the crystallites at high temperatures.

Fully solid state electrochromic displays (ECD) have been prepared several times. But, they all needed more than 1 minute to complete coloring or breaching. Electrochromism of amorphous material is expected to be faster than that of crystalline one by its faster diffusion coefficients of ions due to the open structure. In this study, electrochromic films and a gel electrolyte were made by a sol-gel process using metal salts and alkoxide as raw materials. Tungsten oxide, iridium oxide films and a gel electrolyte were used to fabricate a fully solid state ECD (electrode/tungsten oxide/gel electrolyte/iridium oxide/electrode) and it electrochromic properties were investigated. Crystalline and amorphous tungsten oxide and iridium oxide films were prepared on soda lime silica glass substrates sputter-coated with indium tin oxide (ITO). Electrochromic properties of amorphous WO₃ film were more significant than that of crystalline one. On the other hand, electrochromic properties of amorphous iridium oxide film were less than crystalline one. The ECD showed reversible transmittance modulation of 35% (at 800 nm, film thickness: tungsten oxide 400 nm, iridium oxide 200 nm) under alternative voltage apply of plus or minus 3 V for 0.2 sec. The ECD kept the same transmittance modulation during 200 color-breach cycles.

The manufacturing and operation of window size (30 cm by 90 cm) electrochromic devices is described. Both the electrochromic electrode (WO₃) and the counter electrode (V₂O₅) were deposited by sol-gel method. Electrochromic measurements were performed on both electrodes and the complete device to correlate device performance to fabrication conditions. The paper describes the affects of temperature on the switching characteristics of electrochromic window. The devices were tested in the temperature range between 10 degrees Celsius and 50 degrees Celsius. The switching algorithm described in this paper ensures identical optical performance of electrochromic device in the wide range of temperatures. The algorithm is based on the charge control and does not require monitoring of device transmittance.

A new technique to produce a radial gradient in the refractive index (r-GRIN) in organic-inorganic nanocomposite materials using sol-gel techniques in combination with electrophoretically induced concentration profiles of oxide nanoparticles is presented. The composite material is based on methacryloxylpropyl trimethoxysilane (MPTS), zirconium n- propoxide (ZR), methacrylic acid (MA) and tetraethyleneglycol dimethacrylate (TEGDMA). Irgacure 184 was used as a photosensitive initiator. The surface of these particles is enriched with MA which is linked by a chelating complex to the initial ZR component. The TEGDMA component is used to introduce more flexibility in the organic inorganic network and to reduce polymerization stresses. Electric charges on the ZrO₂ nanoparticle surface force the particles to diffuse in the gel state by electric fields employed by appropriate electrodes in presence of an electric field. The movement and interdiffusion of the Zr-nanoparticles in the matrix were measured by zeta-potential measurements and by photon- correlation spectroscopy (PCS). In the performed experiments, a radial electric field amplitude of 200 V/cm was used and held for 5 hours keeping the material in the gel state. The variation of refractive index in real time was measured by Mach-Zehnder interferometry. After the electrophoretic process, a polymerization step was carried out to immobilize the (Delta) n gradient. (Delta) n was measured by ellipsometry and the value of 0.07 was obtained for a sample of 1 cm in diameter. The form of the concentration profile and hence from the index profile was detected by EDX (energy dispersive x-ray analysis) measurements.

Multi-layer interference filters of surface modified SiO₂- and TiO₂-nanoparticles have been produced on polycarbonat (PC) and on scratch resistant film. AR-coatings (anti-reflex- coatings) were prepared from a dispersion of SiO₂ and TiO₂ colloidal nanoparticles in a hybrid inorganic organic matrix. The TiO₂ particles have been synthesized by addition of HCl and H₂O to a solution of titanium tetraisopropanolate in isopropanol. The SiO₂ nanoparticles were synthesized by base catalyzed hydrolyses and condensation of tetraethoxysilane (TEOS) mixed with an aqueous solvent. The surface modification of the TiO₂ and SiO₂ nanoparticles with 3-glycidoxypropyltrimethoxysilane (GPTS) avoids the agglomeration of the nanoparticles and covalent bonds between the matrix and nanoparticles are formed during a photopolymerization step. The nanoparticles were dispersed in a hydrolyzed GPTS matrix and UVI Cygacure 6974 was added as a photoinitiator. The (lambda) /4 ((lambda) equals 550 nm) films of TiO₂ and SiO₂ sols were prepared on PC and on scratch resistant coated PC by spin-coating techniques. The refractive index of the SiO₂/TiO₂-coatings can be adjusted from 1.47 up to 1.94 depending on the SiO₂ or TiO₂ concentration. By the combination of index matching and photopolymerization, a low temperature interference filter can be realized for plastic substrates with reflection of 0.5% at 550 nm. The coatings show excellent adhesion to the substrates in the cross hatch test and promising mechanical properties.

Sol-gel derived organic-inorganic hybrid materials and their potential for the production of refractive optical elements are presented. The main components of the investigated compositions are precondensed silanes with polymerizable double bonds [e.g. methacryloxypropyltrimethoxysilane (MPTS)] and co-condensates thereof. Dimethacrylates like tetraethyleneglycoldimethacrylate (TEGDMA) were employed as organic monomers. Molar ratios of silanes to organic monomers between 10:90 and 90:10 were investigated. Nanoscaled titania was incorporated in the homogeneous mixture of silanes and organic monomers. The combination of different molecular hybrid matrices and inorganic nanoparticles allows the adjustment of material properties, for example: impact strength between 2 and 15 kJ/m², Youngs moduli between 0.8 and 3.7 GPa and universal hardness in the range from 40 to 170 N/mm². Phase separation could be kept in the nanometer range to minimize optical losses due to scattering effects. Depending on composition, n_e could be varied between 1.50 and 1.54, whereby the corresponding Abbe numbers ranged from 57 to 45. Ophthalmic lenses were prepared in less than 10 hours by simple mould techniques and by applying a combination of photochemical and thermal curing processes.

A novel nanocomposite lithium ion-conducting electrolyte has been developed, based on organically modified silanes, which is suitable for application in a sol-gel electrochromic system. The system developed consists of FTO-coated (fluorine doped tin oxide) glass coated with tungsten oxide, WO₃, at one side of the device as the electrochromic layer, with a cerium oxide-titanium oxide layer, CeO₂-TiO₂, acting as ion-storage layer or counter electrode. The adhesive properties of the electrolyte enabled the manufacture of electrochromic devices in a laminated structure: glass\FTO\WO₃\nanocomp.elect.\CeO₂-TiO₂\FTO\glass. The conductivity of the nanocomposite electrolyte system varies between 10^-4 and 10^-5 Scm^-1 at 25 degrees Celsius depending on the exact composition. The temperature dependence of the conductivity exhibits typical Vogel-Tamman-Fulcher (VTF) behavior. The thickness of the electrolyte between the two halves of the device could be adjusted by the use of a spacer technique in the range 10 - 150 micrometer. Optoelectrochemical measurements were conducted on electrochromic devices to study the kinetics of coloration and bleaching as a function of the number of switching cycles. At present, cells are constructed in two formats: 10 multiplied by 15 cm² and 35 multiplied by 35 cm². Switching times under one minute were achieved for the smaller format with a corresponding optical modulation between 75% to 20% (at lambda equals 0.633 micrometer). In the case of the larger format the switching time increases to several minutes due to the increase in geometric area.

A new synthesis and processing route for SiO₂ glass like micropatterns with heights up to 30 micrometer by gel embossing and thermal densification has been developed. For this reason an organically modified nanoparticulate sol prepared by acid catalysis of methyl- and phenyl- triethoxysilane and tetraethyl orthosilicate in combination with colloidal silica sol was used. Sol coatings with thicknesses up to 15 micrometer are obtained by dipping of float glass substrates. After a predrying step of about 60 s micropatterns are obtained using a pressure of only 2.5 mN/mm². Due to this low pressure, flexible and low cost silicon rubber stampers can be used. The gelation time of the sol can be extended from 5 d to 16 days and the working time for embossing can be extended from 60 s up to 100 s by a partial replacement of methyl silane by phenyl silane from 0 to 20 mole %. After embossing and drying at 50 degrees Celsius the patterned layer was densified at temperatures up to 500 degrees Celsius to 95% density as indicated by refractive index measurements. It is assumed that the densification process is strongly promoted by the used colloidal silica nano particles. The linear shrinkage of the micropatterns is limited to about 25% due to the high solid content of the sol and the high green density of the layers. Since the structures are densified at temperatures far below T_g sharp edged patterns can be obtained as shown by high resolution secondary electron microscopy. The capability of this technique is demonstrated by the fabrication of light trapping structures with pyramides of 7 micrometer in height and 10 micrometer in width on an area of 20 multiplied by 20 mm² and micro lens arrays of lenses with 30 micrometer in height and 600 micrometer in diameter on an area of 20 multiplied by 30 mm².

Transparent inorganic/organic hybrids containing various inorganic components have been synthesized from modified metal alkoxides and silanol-terminated polydimetylsiloxane (PDMS). The chemical modification of metal alkoxides with chelating ligands was carried out in order to prevent the precipitation during hydrolysis and condensation. The chemical modification and hydrolysis reaction were investigated by IR and NMR spectroscopic methods. The formation of transparent hybrids was found to be influenced by the inorganic source and M(OR)_n/PDMS ratio. The transparent hybrids were flexible, indicating the storage modulus from 10⁶ to 10⁸ Pa at room temperatures. It increased with the increase in valence number of the inorganic components. The hybrids were transparent in the visible wavelength region, especially long- wavelength region. The refractive index of the hybrids linearly increased with increasing the inorganic content. The refractive index was also dependent on the inorganic component derived from metal alkoxides. It increased with valence of metallic elements in the inorganic components, in the order Al < Zr <EQ Ti < Ta <EQ Nb.

A wide variety of biomolecules have been incorporated into sol-gel matrices, retaining their ability to function once immobilized. The interactions required for their activity occur within the macromolecular structure of these dopants. As a result, there is relatively little known about impact of the silicate matrix on fundamental recognition events. To investigate thai effects of the silicate matrix upon the specific hydrogen bond recognition between an immobilized species and a substrate at the molecular level, we have incorporated the biological cofactor flavin mononucleotide (FMN) into a silicate matrix. Molecular recognition of the flavin isoalloxazine unit immobilized within the gel cybotactic regions has been investigated via co-doping with a synthetic diaminopyridine receptor. The presence and specificity of the host-guest interaction was established via quenching of the flavin fluorophore by the receptor, and complete absence of quenching by a non-hydrogen bonding control. The degree of recognition achieved was quantified via fluorescence titration, demonstrating significantly enhanced binding relative to methanolic solution. Investigations into this recognition proces are discussed.

CEA Limeil-Valenton has embarked in a project called 'laser megajoule' (LMJ) consisting of the construction of a 2-MJ/500- TW (351-nm) pulsed Nd:glass laser and devoted to inertial confinement fusion research in France. Room temperature and atmospheric pressure deposited sol-gel coatings for antireflective (AR), highly reflective (HR) and polarizer uses, and silicone films for environmental protection have displayed remarkable optical and laser strength performance. Such coatings can be applied onto large area and at a low cost compared to conventional vacuum deposition techniques. CEA Limeil-Valenton is also maintaining sustained efforts to promote the sol-gel technology in other areas.