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Recent interest in photolithographic processes employing single and two-photon absorption processes have afforded advanced opportunities to fabricate both planar and three-dimensional microstructures. The fabrication of such structures is dependent on the local polymerization of the organic moieties using photoinitiating molecules, and a key parameter to consider is the dependency of the photoreactivity of these initiators on the matrices in which they are dispersed. To our knowledge, there has been no comprehensive investigation reported on the photoreactivity dependency of commercially available photoinitiators inserted within hybrid sol-gel materials. The aim of this paper is to highlight and explain the influence of the composition of hybrid organic-inorganic sol-gel materials on the photoreactivity of UV-sensitive initiators. Of particular interest is the understanding of the interactions between photoinitiating molecules and the sol-gel matrix. It is shown that both the nature of the chelating agent as well as the degree of chelation of the inorganic part of the hybrid sol-gel material significantly influence the spectral absorption of the photoinitiator. It is demonstrated that metal-ligand charge transfer processes are the main phenomena responsible for the red shift of the absorption of the amino-functionalized photoinitiators, which is strongly dependent on the condensation of the materials. [ABSTRACT FROM AUTHOR]

Sol-gel-derived silica films were fabricated by dip-coating onto planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence is quenched in the presence of oxygen. The structure and behaviour of sol-gel films is related to the fabrication parameters. In order to optimise the films for oxygen sensing in gaseous and in aqueous media, the quenching behaviour was monitored as a function of dip-speed and water: precursor ratio. By adjusting the above parameters, film properties can be tailored to optimise oxygen quenching in particular concentration ranges and environments. [ABSTRACT FROM AUTHOR]

Tetraethoxysilane (TEOS) sol-gel monoliths impregnated with three different luminescent [Ru( L)3]2+ complexes (where L=2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,7-diphenyl,1,10-phenanthroline (dpp)) have been prepared. The photoluminescence properties of these complexes were followed as a function of time, as the sol-gel reactions proceeded. Clear differences were observed in the emission energies and the emission lifetimes of the complexes upon gel formation. These differences can be explained by the different extent of electrostatic interaction between the surface of the siloxane polymer and the immobilised complex. [ABSTRACT FROM AUTHOR]

Two samples of cronstedtite, a mixed valence serpentine with ideal formula {Fe,Fe}[Si,Fe]O(OH), have been examined by X-ray and neutron diffraction, thermopiezic analysis, magnetization and susceptibility measurements and Mössbauer spectroscopy. The conductivity is thermally activated, with activation energies of 0.25 eV in the basal plane and 0.37 eV in the perpendicular direction. The shape of paramagnetic Mössbauer spectra above 200 K is influenced by charge fluctuations in octahedral sites and fits of spectra at temperatures up to 410 K with a stochastic relaxation model give an activation energy of 0.19 eV. Static charge ordering sets in progressively below about 100 K. Cronstedtite orders antiferromagnetically below 12 K in a structure with antiferromagnetic octahedral sheets and moments perpendicular to the a-axis. Magnetic and charge-ordered structures are proposed for the ideal composition. [ABSTRACT FROM AUTHOR]