Inverse opal films of molecularly imprinted polymers (MIP) were elaborated using the colloidal crystal template method. The colloidal crystals of silica particles were built by the Langmuir-Blodgett technique, allowing a perfect control of the film thickness. Polymerization in the interspaces of the colloidal crystal in the presence of bisphenol A (BPA) and removal of the used template provides 3D-ordered macroporous methacrylic acid-based hydrogel films in which nanocavities derived from bisphenol A are distributed within the thin walls of the inverse opal hydrogel. The equilibrium swelling properties of the nonimprinted (NIPs) and molecularly imprinted polymers (MIPs) were studied as a function of pH and bisphenol A concentration, while the molecular structures of the bulk hydrogels were analyzed using a cross-linked network structure theory. This study showed an increase in nanopore (mesh) size in the MIPs after BPA extraction as compared to NIPs, in agreement with the presence of nanocavities left by the molecular imprints of the template molecule. The resulting inverse opals were found to display large responses to external stimuli (pH or BPA) with Bragg diffraction peak shifts depending upon the hydrogel film thickness. The film thickness was therefore shown to be a critical parameter for improving the sensing capacities of inverse opal hydrogel films deposited on a substrate.

Pyroelectric energy conversion offers a way to convert waste heat directly into electricity. It makes use of the pyroelectric ef-

4 pagesInternational audienceThis paper describes the introduction of a planar defect layer within inverse opal hydrogels for the elaboration of tunable photonic crystal pH sensors with enhanced optical properties. We demonstrate a mechanically robust, highly sensitive and fast response photonic crystal fabricated by a stepwise strategy combining the Langmuir-Blodgett technique and the photonic crystal template method. The resulting material consists of a three-dimensional, highly-ordered and interconnected macroporous array of poly(methacrylic acid), which is a hydrogel sensitive to pH. The optical properties of these inverse opals were investigated using reflection spectroscopy. The defect layer was shown to enhance both the sensitivity and the response time of the photonic crystal sensing materials

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We describe the plasmonic properties of a two-dimensional periodic metallic grating of macroscopic size obtained by gold deposition on a self-assembled silica opal. Structural characterization shows a transition from microscopic order to isotropy at macroscopic scale. Optical reflection spectra exhibit a dip of almost complete absorption due to coupling to surface-plasmon-polaritons (SPP). This is explained by theoretical calculations introducing a density of coupled SPP modes. We demonstrate, at a given incidence angle, a broad continuum of coupled wavelengths over the visible spectrum. This opens new possibilities in fields where light-plasmon coupling is required over a broad range of wavelengths and incidence orientations.

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We experimentally measure and analytically describe the fluorescence enhancement obtained by depositing CdSe/CdS nanocrystals onto a gold plasmonic crystal, a two-dimensional grating of macroscopic size obtained by gold deposition on a self-assembled opal. We show evidences of nanocrystals near-field coupling to the gold Surface Plasmons Polaritons (SPP) followed by grating-induced SPP re-emission to far-field. We develop a theoretical framework and an original method in order to evaluate, from photoluminescence experiments, the SPP extraction efficiency of a grating.

The emission spectrum of the trion state in very thick shell CdSe/CdS nanocrystals is characterized at 4 K by photon correlation Fourier spectroscopy. A value of 50 μeV for the width of the zero phonon line is measured. The absence of blinking and the high photostability of these emitters offer the possibility to investigate the dynamics of the emission spectrum at a time scale as short as 250 ns. We show that the high value of the linewidth (50 μeV) is not due to spectral diffusion induced by the close environment of the emitter at time scales larger than 250 ns. The broadening is attributed to the additional third carrier when compared to the monoexcitonic state.