Frédéric Chaput

Perylene- and pyrromethene-doped xerogel for a pulsed laser

Hydrophobic photostable dye molecules such as perylenes or pyrromethenes were trapped in xerogel matrices. Using these new materials as solid-state dye lasers, we have demonstrated efficient laser operation. Slope efficiencies of up to 30% were obtained in the millijoule output-energy range. Tunabilities of up to 60 nm were observed, and more than 150,000 pulses were emitted by the same spot of a given sample when the laser was pumped at millijoule energy levels.

Photostability of dye molecules trapped in solid matrices

The photostability of dye molecules trapped in transparent solid matrices synthesized by the solgel technique was studied both experimentally and theoretically using a model with numerical and approximate analytical solutions. The model is based on a one-photon photodestruction process with the creation of an absorbing bleached molecule. We give the number of photons that different trapped dye molecules can absorb on average before they are bleached. Dyes such as Perylene Red, Perylene Orange, Pyrromethenes 567 and 597, Rhodamines 6G and B, DCM, a Xanthylium salt, and Neon Red were investigated; significant differences were observed. Some dye molecules in solvents were also studied; increased stability resulted when the molecules were trapped in solid matrices.

Toward millions of laser pulses with pyrromethene- and perylene-doped xerogels

Significant improvements have been obtained for solid-state dye lasers with doped xerogels. By using longitudinal pumping with a frequency-doubled Q-switched Nd: YAG laser, we obtained as much as 86% slope efficiency and 5 x 10(5) pulses lifetime. Furthermore, newly prepared deoxygenated samples exhibited even greater lifetimes.

Reverse saturable absorption in solid xerogel matrices

Aluminophthalocyanine (APC) and fullerene carbon 60 (C60) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C60. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matrix.Aluminophthalocyanine (APC) and fullerene carbon 60 (C60) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C60. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matrix.

Luminescence and Scintillation Properties at the Nanoscale

This contribution is a review of the luminescence and scintillation properties of nanoparticles (NP), particularly doped insulators. Luminescence spectroscopy is an appropriate tool to probe matter at the nanoscale. Luminescence is also the last stage of the scintillation process. Specific surface and structural effects occurring in NP are reported. Their consequences on the NP luminescence properties are discussed. Parts of the effects are related to the preparation method. On the other hand some intrinsic properties of the nanostructures which can modify the optical properties are described: quantum confinement and dielectric confinement. The response under high-energy excitation is also discussed. It appears that their size can be used as a tool to describe the spatial distribution of electronic excitations induced by the relaxation process after the high-energy excitation. Finally, potentiality to grow transparent bulk materials based on small Nps agglomeration via soft chemistry route is presented. It is a promising approach toward the development of scintillating materials.

Magnetically textured γ-Fe2O3 nanoparticles in a silica gel matrix: Structural and magnetic properties

This paper is devoted to magnetic and structural properties of anisotropic γ-Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the r...

Effect of chromophore–chromophore electrostatic interactions in the NLO response of functionalized organic–inorganic sol–gel materials ☆

Abstract In the last years, important non-linear optical (NLO) results on sol–gel and polymeric materials have been reported, with values comparable to those found in crystals. These new materials contain push–pull chromophores either incorporated as guest in a high T g polymeric matrix (doped polymers) or grafted onto the polymeric matrix. These systems present several advantages, however they require significant improvement at the molecular level—by designing optimized chromophores with very large molecular figure of merit, specific to each application targeted. Besides, it was recently stated in polymers that the chromophore–chromophore electrostatic interactions, which are dependent of chromophore concentration, have a strong effect into their NLO properties. This has not been explored at all in sol–gel systems. In this work, the sol–gel route was used to prepare hybrid organic–inorganic thin films with different NLO chromophores grafted into the skeleton matrix. Combining a molecular engineering strategy for getting a larger molecular figure of merit and by controlling the intermolecular dipole–dipole interactions through both: the tuning of the push–pull chromophore concentration and the control of tetraethoxysilane concentration, we have obtained a r 33 coefficient around 15 pm/V at 633 nm for the classical DR1 azo-chromophore and a r 33 around 50 pm/V at 831 nm for a new optimized chromophore structure.

Synthesis, electron tomography and single-particle optical response of twisted gold nano-bipyramids.

A great number of works focus their interest on the study of gold nanoparticle plasmonic properties. Among those, sharp nanostructures appear to exhibit the more interesting features for further developments. In this paper, a complete study on bipyramidal-like gold nanostructures is presented. The nano-objects are prepared in high yield using an original method. This chemical process enables a precise control of the shape and the size of the particles. The specific photophysical properties of gold bipyramids in suspension are ripened by recording the plasmonic response of single and isolated objects. Resulting extinction spectra are precisely correlated to their geometrical structure by mean of electron tomography at the single-particle level. The interplay between the geometrical structure and the optical properties of twisted gold bipyramids is further discussed on the basis of numerical calculations. The influence of several parameters is explored such as the structural aspect ratio or the tip truncation. In the case of an incident excitation polarized along the particle long axis, this study shows how the plasmon resonance position can be sensitive to these parameters and how it can then be efficiently tuned on a large wavelength range.

Synthesis of PEGylated gold nanostars and bipyramids for intracellular uptake

A great number of works have focused their research on the synthesis, design and optical properties of gold nanoparticles for potential biological applications (bioimaging, biosensing). For this kind of application, sharp gold nanostructures appear to exhibit the more interesting features since their surface plasmon bands are very sensitive to the surrounding medium. In this paper, a complete study of PEGylated gold nanostars and PEGylated bipyramidal-like nanostructures is presented. The nanoparticles are prepared in high yield and their surfaces are covered with a biocompatible polymer. The photophysical properties of gold bipyramids and nanostars, in suspension, are correlated with the optical response of single and isolated objects. The resulting spectra of isolated gold nanoparticles are subsequently correlated to their geometrical structure by transmission electron microscopy. Finally, the PEGylated gold nanoparticles were incubated with melanoma B16-F10 cells. Dark-field microscopy showed that the biocompatible gold nanoparticles were easily internalized and most of them localized within the cells.

WO3 nanorods created by self-assembly of highly crystalline nanowires under hydrothermal conditions.

WO3 nanorods and wires were obtained via hydrothermal synthesis using sodium tungstate as a precursor and either oxalic acid, citric acid, or poly(methacrylic acid) as a stabilizing agent. Transmission electron microscopy images showed that the organic acids with different numbers of carboxylic groups per molecule influence the final sizes and stacking nanostructures of WO3 wires. Three-dimensional electron diffraction tomography of a single nanocrystal revealed a hexagonal WO3 structure with preferential growth along the c-axis, which was confirmed by high-resolution transmission electron microscopy. WO3 nanowires were also spin-coated onto an indium tin oxide/glass conducting substrate, resulting in the formation of a film that was characterized by scanning electron microscopy. Finally, cyclic voltammetry measurements performed on the WO3 thin film showed voltammograms typical for the WO3 redox process.