Nathalie Sanz

Organic nanocrystals grown in sol–gelcoatings

Well-defined organic crystals have been grown in inorganic gel coatings with particle sizes in the submicron range and narrow size distributions. The direct characterisation of these hybrid organic–inorganic films by optical confocal microscopy has allowed elucidation of the role of the main experimental parameters such as the nature of the gel precursors or solvents, the organic doping level and the rotation speed of the spin-coating apparatus. This is a one-step process in which nucleation and growth of the organic crystals occur simultaneously with the formation of the gel framework. Nanocrystallisation is optimised through the control of the coupling effect between the three elementary processes: nucleation, growth and matrix polymerisation. The validity and reproducibility of this simple and generic method have been demonstrated through the use of several organic molecules, solvents and silicon alkoxides.

Organic nanocrystals grown in gel glasses for optical-power-limiting applications

Nonlinear absorption and optical-limiting properties of sol–gel glasses doped with nanocrystals of stilbene 3 have been studied. These organic–inorganic nanocomposite materials can be highly doped (up to 30 wt %) with active molecules through the control of nanometer-scale crystallization. In the nanosecond time regime, the nonlinear absorption occurs in a two-step process, which is characterized by two-photon absorption and excited-state absorption spectroscopies. In a F/5 optical system, the output energy is damped below 20 μJ for all visible wavelengths, 6 μJ at λ=600 nm. Thus, these nanocomposite materials are a good alternative both to concentrated solutions, due to their stability, and to crystals, due to their isotropic response with polarization.

Confined nucleation and growth of organic nanocrystals in sol–gel matrices

We have engineered new hybrid organic–inorganic materials through a simple and generic preparation of stable organic nanocrystals grown in gel–glass matrices. This process was based on confined nucleation and growth of dyes in the pores of dense gels. For bulk samples, narrow size distributions of particles were obtained between 10 and 20 nm in diameter. We extended this method to the preparation of organic nanocrystals embedded in sol–gel thin films by spin-coating. For all these nanocomposite samples, we significantly increased the dye stability and obtained promising optical properties (luminescence, NLO properties, SHG). Moreover we also demonstrated the basic working principles of a new type of fluorescent nanosensors through the preparation of organic luminescent nanocrystals grown in silicate films.

Organic nanocrystals grown in sol–gel matrices: a new type of hybrid material for optics

We have engineered new hybrid organic–inorganic materials through a simple and generic preparation of stable organic nanocrystals grown in gel–glass matrices. This process is based on the confined nucleation and growth of dyes in the pores of dense gels. For bulk samples, narrow size distributions of particles are obtained between 10 and 20 nm in diameter. We have extended this method to the preparation of organic nanocrystals embedded in sol–gel thin films by spin-coating. For all these nanocomposite samples, we have significantly increased the stability of the dye and obtained promising linear and nonlinear optical properties. To cite this article: J. Zaccaro et al., C. R. Physique 3 (2002) 463–478.

Electric-field induced orientation of organic nanocrystals in sol-gel matrix

Abstract Organic nanocrystals embedded in sol–gel glasses are studied for quadratic nonlinear optical applications. Thermally assisted electric field poling is employed to orient nanocrystals thin films. The evolution of second-order susceptibility is monitored by in situ second-harmonic generation. Although it was possible to create some degree of noncentrosymmetric order, the orientation process is found to be hindered by the strong conductivity of the matrix and the nanocrystals–matrix interactions.

Organic nanocrystals grown in sol–gel matrices: new hybrid organic–inorganic materials for optics

We have developed a simple and generic preparation of stable organic nanocry stals grown in gel-glass matrices. The synthesis of these hybrid organic-inorganic materials is based on the confined nucleation and growth of organic phases in the pores of dense gels. For bulk nanocomposite samples, narrow size distributions of particles (10–20 nm in diameter) are obtained. We have extended this method to the preparation of organic nanocrystals embedded in sol-gel thin films prepared by spin-coating. For all these nanocomposite materials, we have significantly increased the dye stability and obtained promising optical properties: luminescence, non-linear optical properties or photochromism. Moreover, we have also demonstrated basic working principles of a new type of fluorescent nanosensor through the preparation of organic luminescent nanocrystals grown in silicate films.

Molecular nanocrystals grown in sol-gel thin films for ultrabright chemical sensor applications

Polyaromatic dyes were used to synthesize molecular nanocrystals in sol-gel thin films for sensor applications. Fluorescence Confocal Microscopy (FCM) and Transmission Electron Microscopy (TEM) experiments showed the advantages of our nanocrystallization process compared with microcrystallization in free solutions. Indeed, we obtained well-dispersed and spherical nanocrystals with a narrow size distribution, exhibiting a good crystallinity. Time-resolved fluorescence spectroscopy allowed us to measure fluorescence lifetimes of nanocrystals in presence of molecular probes. Then, chemical sensoring properties of these molecular nanocrystals were demonstrated.

Multilayer two-dimensional arrays of organic nanocrystals for 3-D optical data storage

We have developed a new type of hybrid organic-inorganic materials constituted of organic nanocrystals embedded in silicate matrices. They are prepared by a generic process based on the confined nucleation of molecular crystals in the pores of sol-gel matrices, bulk or thin films. In this study, we have controlled the spatial distribution of organic nanocrystals in sol-gel thin films prepared by spin-coating. This spatial control of nucleation is obtained by assisting the nanocrystallisation process through nanostructured substrates. Substrates exhibit arrays of wells where the dye nucleates when the initial solution is deposited. The 3-D spatial control is achieved through a multilayer process. This nucleation control gives an opportunity to design new 3-D optical data storage or 2-D arrays of luminescent crystals for chemical or biological sensor applications.

New type of nanocomposite material for optical applications: organic nanocrystals in sol-gel glasses

We present a new type of composite materials that we have designed for optical applications: sol-gel glasses highly doped with organic nanocrystals. The nanosized control of crystallization allows us to obtain optical grade samples with very high concentrations of active molecules. Here, we report on the optical limiting properties of bulk glasses doped with stilbene 3 nanocrystals, and on the second-harmonic generation of thin films doped with oriented nonlinear nanocrystals.