Optical properties of Co2+-doped silica gel monoliths

International audienc

Magnetic Study of SiO2/γ-Fe2O3 Nanocomposites Prepared by the SOL-GEL Method

Nanocomposites of γ-Fe2O3 in a silica matrix were prepared by the sol-gel method using tetramethylorthosilicate (TMOS) as a precursor of silica and introducing iron as Fe(NO3)3 with Fe/Si ratios of 2, 5, 10 and 20%. The obtained gels were calcinated at temperatures between 600°C and 1000°C. Magnetic measurements performed with a vibrating magnetometer showed that superparamagnetic γ-Fe2O3 nanoparticles began to form at 700°C as confirmed by X-rays and Mössbauer spectroscopy. Superparamagnetic magnetization curves were fitted by a Langevin function considering a log-normal particle size distribution. This allowed to determine the saturation magnetization and the particle size distribution of the samples. The latter results were in good agreement with observations made by Transmission Electronic Microscope. For all studied concentrations, the γ-Fe2O3 particles size increased with the calcination temperature up to a maximal average diameter of 40 Å. This maximum was reached at 900°C for the highest concentrations and l000°C for the lowest. Calcinations at higher temperatures led to the degradation of the γ-Fe2O3 phase with creation of defects in the particles and formation of α-Fe2O3. This phenomenon was accompanied by a decrease in the saturation magnetization and the presence of an hysteresis in the magnetization curve

SINTERING STUDY OF SOME FINE POWDERS OF BaTiO3 AND DIELECTRIC COMPOSITIONS

La possibilité d'obtenir des titanates de type BaTiO3 par synthèse chimique à basse température conduit à des poudres fines submicroniques. On compare l'aptitude au frittage de poudres de BaTiO3 préparées suivant plusieurs méthodes relevant de la coprécipitation ou du sol-gel. Les relations entre granulométrie (0.1 µm), températures de frittage (800°C) et densité finale (96% dth) sont analysées et montrent la possibilité d'obtenir des nuances de BaTiO3 pures à bas point de frittage. Les résultats concernant des céramiques mixtes Ba1-xSrxTiO3 seront donnés et comparés aux céramiques obtenues par les méthodes classiques de chamotage et broyage.The possibility of chemical synthesis of titanates such as BaTiO3 and at low temperature leads to the preparation of submicronic, fine powders. The sinterability of BaTiO3 powders prepared by several chemical methods such as coprecipitation or sol-gel are compared. Relations between grain size (0.1 µm), sintering temperatures (800°C) and final density (near to 96% dth) are examined and show the possibility to obtain BaTiO3 powders, pure and having low sintering température. Results about ceramics with formulae : Bai-xSrxTiO3 are proposed and compared to ceramics synthetized by classical methods such as high temperature diffusion and grinding

Investigation of laser ablation on hybrid sol-gel material applied to the field of microoptics

International audienc

Two-photon excitation in the life sciences: From observation to action

International audienceTwo-photon (TP) excitation of organic chromophores is of great interest for decades, as applications of such phenomena from 3-dimentional (3D) microfabrication to optical limiting and optical data storage, are of increasing importance. More recently, two-photon excitation found important applications in biology, notably in two-photon excited microscopy (TPEM) or two-photon photodynamic therapy (2P-PDT). Nevertheless, these techniques were using dyes or sensitizers designed for one-photon processes with low two-photon response. The lack of efficient molecules specifically designed for two-photon applications has led us to design new chromophores for biological applications with increased sensitivity to two-photon excitation and specifically added properties useful in biological media, such as water solubility. Here we describe the molecular engineering of such dyes mainly for cell and small animal observation by TPEM and their conjugation to magnetic nanoparticles and bio-nanoparticles such as viruses.We will then focus on the possibility to use photochemical reaction for cell triggering by two-photon photorelease of biologically active substances the so-called two-photon uncaging