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Hybrid silica-based sol-gel films containing Disperse Red 1 (DR1), carbazole units (CBZ) and 2,4,7-trinitro-9-fluorenone (TNF) at different concentrations show reversible photoinduced birefringence. Polarization sensitive holographic gratings have been produced and characterized. Dichroism measurements give information on the orientation mechanisms and on the aggregation of the dye molecules. The alignment of the DR1 molecules by corona poling is verified by second harmonic generation (SHG) and a moving grating technique is used to investigate an asymmetric energy exchange in a two-beam coupling experiment, typical of photorefractive gratings.Hybrid silica-based sol-gel films containing Disperse Red 1 (DR1), carbazole units (CBZ) and 2,4,7-trinitro-9-fluorenone (TNF) at different concentrations show reversible photoinduced birefringence. Polarization sensitive holographic gratings have been produced and characterized. Dichroism measurements give information on the orientation mechanisms and on the aggregation of the dye molecules. The alignment of the DR1 molecules by corona poling is verified by second harmonic generation (SHG) and a moving grating technique is used to investigate an asymmetric energy exchange in a two-beam coupling experiment, typical of photorefractive gratings.

AbstractThe lamproite of Gaussberg is an ultrapotassic rock where leucite, olivine and clinopyroxene microphenocrysts occur in a glass-rich groundmass, containing microliths of leucite, clinopyroxene, apatite, phlogopite and rare K-richterite.Abundant silicate melt inclusions occur in olivine, leucite and, rarely, in clinopyroxene microphenocrysts. Raman investigations on melt inclusions showed the presence of pure CO2in the shrinkage bubbles. On the other hand, the glass of the groundmass is CO2-poor and contains up to 0.70 wt.% of dissolved H2O, as estimated by infrared spectra. It is inferred that CO2was released at every stage of evolution of the lamproite magma (CO2-rich shrinkage bubbles), whereas H2O was retained for longer in the liquid. At Gaussberg, CO2seems to have a major role at relatively high pressure where it favoured the crystallization of H2O-poor microphenocrysts; the uprise of the magma to the surface decreased the solubility of CO2and caused a relative increase in water activity. As a consequence, phlogopite and K-richterite appeared in the groundmass.The glass composition of both the groundmass and melt inclusions suggests different evolutions for the residual liquids of the investigated samples. Sample G886 shows the typical evolution of a lamproite magma, where the residual liquid evolves toward peralkaline and Na-rich composition and crystallizes K-richterite in the latest stage. Sample G895 derives from mixing/mingling of different batches of magma; effectively glasses from melt inclusions in leucite and clinopyroxene are more alkaline than those found in early crystallized olivine. Leucite and clinopyroxene crystallized early from a relatively more alkaline batch of lamproite magma and, successively, a less alkaline, olivinebearing magma batch assimilated them during its rise to the surface.

Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel dip-coating process. The effect of acetylacetone, diethanolamine and polyethylene glycol on the structure of the heat-treated titania films was examined by Raman and FTIR spectroscopy and X-ray diffraction. The effect the complexing agents have on the anatase to rutile phase transition during the heat treatment process is studied. The understanding of this effect is expected to enhance our capacity to tailor the composition and morphology of films and thus their properties. The Raman and the infrared spectra of nanocrystalline titania films and the changes induced by the heat treatment were also investigated. We have also studied the size of the crystallites in TiO$\_2$ films and its dependence on the type of complexing agent used.

TiO$\_2$ nanocrystalline thin films with varying degree of porosity have been prepared using a low temperature method. TiO$\_2$ films of the anatase form have been obtained by using a polyethylene glycol (PEG) modified sol-gel method. Densification and crystallization of the films was found to result from the thermal treatment of the dip coated films in boiling water. The films have been characterized by Raman, XRD, FTIR, AFM and optical methods. Highly transparent films with transmission in excess of 85% and porosity as high as 58% are formed predominantly of anatase crystallites of dimensions of the order of 5 nm. Initial results on lithium intercalation into these films resulting in an efficient optical modulation in the visible and near infrared regions demonstrate a good potential of these films for electrochromic applications.

The chemical properties of Disperse Red 1 (DR1), a dye molecule commonly used as an active guest of thin silica or ORMOSILs films for optical applications, were investigated by micro-Raman spectroscopy. The influence of the acid catalyst was studied in DR1 + TEOS (tetraethyl orthosilicate), DR1 + TEOS + GLYMO (3-glycidoxypropyltrimethoxysilane) and DR1 + TEOS + ICPTEOS [3-(triethoxysilyl)propyl isocyanate] sol–gel starting solutions and on the corresponding bulk glasses. A protonated form of DR1 was found in some glasses, and its Raman spectrum is reported. The protonation is not observed in GLYMO-based matrices owing to the protection against acid attack provided by the epoxy group. Copyright © 2000 John Wiley & Sons, Ltd.

Films and powders of iron oxide (Fe2O3) prepared by two different sol–gel syntheses, starting from Fe(NO3)3·9H2O or FeCl3·6H2O, were investigated by Raman microscopy. Different phases with different morphology were produced according to the preparation. The spectra obtained in the micro-Raman configuration were compared with the ambiguous data in the literature given by conventional Raman techniques. The principal difficulty in the correct interpretation of the Raman spectrum of the iron oxides is the co-existence of different phases. Contradictory results are also explained by laser–induced thermal effects which easily change the wavenumbers and lineshapes of the phonons. A Stokes–Anti-Stokes procedure was utilized to control the local temperature during the measurement and also for calibration of the wavenumbers. The micro-Raman spectra of hematite, magnetite and other iron oxides are presented and compared with literature data. Copyright © 1999 John Wiley & Sons, Ltd.

The evolution of the Raman spectrum of 3-(trimethoxysilyl)propyl methacrylate (TMSPM) during polymerization processes which take place in different chemical reactions is reported. TMSPM is a monomer which has both a methoxide function and a carbon–carbon double bond and is of great interest as precursor to obtain organic–inorganic hybrid glasses hosting chromophores or optically active molecules for a large variety of photonic applications. By changing the reaction conditions, the hydrolysis of TMSPM is achieved by means of polar solvents, or an organic polymerization by using a radical starter: according to the process, the optical, mechanical and chemical properties of the final product show large variations which can be tailored for specific uses. These reactions were monitored through micro-Raman spectroscopy and a correlation between the vibrational spectra and the degree of organic and inorganic polymerization was obtained. Copyright © 1999 John Wiley & Sons, Ltd.

Cadmium titanate (CdTiO3) has been prepared by a room-temperature sol-gel technique. The powders were characterized by means of X-Ray Diffraction. Samples treated at 800°C give rise only to the ilmenite-like phase, but, after a treatment at 1100°C for about four hours, the orthorhombic perovskite is the only crystalline phase observed. The Raman spectrum of the perovskite phase is reported for the first time and that of the ilmenite phase is compared with the spectrum of CdTiO3bulk crystals. The effects of the starting stoichiometry on the purity of the final phases, relative to the presence of TiO2(anatase and rutile) or CdO, are investigated.

The sol-gel preparation of PbTiO3by two different methods is reported. Both methods began with titanium isopropoxide and lead acetate as organic precursors, but without or with hydrochloric acid as catalyst, respectively. Preparation procedures and working atmosphere also differred. The crystallization by thermal treatments and laser annealing was followed by XRD and Raman spectroscopy. When no hydrochloric acid was used, an intermediate pyrochlore phase, Pb2Ti2O6, was observed during the thermal treatment, and the final perovskite was obtained together with PbTi3O7as the minor phase. Using the catalyst, the pure perovskite, PbTiO3, was obtained through an unidentified phase appearing at the beginning of the crystallization process. Frequency changes in the Raman spectra during the crystallization are attributed to pressure effects on the microcrystals.

The short range order around Ti atoms in sol-gel derived bulk amorphous TiO2is investigated by X-Ray Absorption Spectroscopy (EXAFS and XANES). Two TiO distances are found: the longer distance is attributed to the presence of anatase micro-crystallites, whereas the shorter one is due to a residual of the alkoxide precursor. XANES measurements give no evidence of tetrahedrally coordinated Ti, both in the organic precursor or in the amorphous phase. The X-Ray absorption data confirm that thermal treatments up to 350°C on bulk amorphous TiO2give crystalline anatase and up to 750°C give crystalline rutile.

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The preparation by the sol-gel method of bulk vitreous TiO2 is reported and its transformation both by controlled thermal treatment and by laser-induced heating in the anatase and rutile crystalline forms is studied by Raman spectroscopy. The results are compared with those existing for amorphous TiO2 thin films. The dependence of the Raman frequencies and linewidths on the incident laser power is presented and the Raman spectrum of the brookite (a third naturally occurring form of TiO2) is also reported as a comparison.

Sol-gel-derived bulk amorphous TiO2and the crystalline phases obtained by heat treatments are investigated by X-ray absorption spectroscopy. The environment of the Ti atoms in the amorphous phase shows a residual from the alkoxide precursor and the presence of anatase crystallites. Thermal treatments up to 350°C give crystalline anatase and the pure rutile phase is obtained at 750°C. Near-edge absorption measurements confirm the octahedral coordination of Ti in all the phases investigated.

Raman spectra have been obtained for 2Bi2O33[(GeO2)x(SiO2)1 - x] (2–3 composition) and 6Bi2O3[(GeO2)x(SiO2)1 - x] (6-1 composition) glasses at different GeSinominal ratios. In both compositions, the vibrational structure at low frequencies is nearly independent of x. At higher frequencies, typical vibrations are found which may be attributed to GeO and SiO bonds in GeO4and SiO4tetrahedral units, respectively, as observed in mixed crystals with the same stoichiometric formula.

Lead titanate powders obtained by a sol-gel technique have been heat-treated to study the phase transformations from the amorphous to the crystalline state. The process has been investigated by differential thermal analysis, X-ray diffraction and Raman spectroscopy. The sample treated at ≈ 600°C yields the diffraction pattern of a prevalent cubic pyrochlore phase Pb2Ti2O7 - x, together with a minority tetragonal perovskite phase, and the former's Raman spectrum is reported. The metastable paraelectric pyrochlore has only previously been observed in thin films. For heat treatments at higher temperatures, only the ferroelectric perovskite is formed.

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Cadmium titanate (CdTiO3) has been prepared by a room-temperature sol-gel technique. The powders were characterized by means of X-Ray Diffraction. Samples treated at 800°C give rise only to the ilmenite-like phase, but, after a treatment at 1100°C for about four hours, the orthorhombic perovskite is the only crystalline phase observed. The Raman spectrum of the perovskite phase is reported for the first time and that of the ilmenite phase is compared with the spectrum of CdTiO3bulk crystals. The effects of the starting stoichiometry on the purity of the final phases, relative to the presence of TiO2(anatase and rutile) or CdO, are investigated.