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7 pages; International audience; An engineering approach towards combined photonic band gap properties and magnetic functionalities, based on independent nanoscale engineering of two different materials at different length scales, is conceptually presented, backed by simulations, and experimentally confirmed. Large (>200 nm)monodisperse nanospheres of transparent silica self-assemble into a photonic crystal with a visible band gap, which is retained upon infiltration of small (

Coating gold colloids with a well controllable silica shell is finding many applications in the fields of bioconjugation and photonic crystals. In this work, we report on ravine-structured surface morphology changes on silica-coated gold (Au@SiO 2 ) colloids as observed using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) characterizations. These Au@SiO 2 colloids were prepared in the direct Stober synthetic route and the silica-shell thickness was varied between 20 to 100 nm. An aggregation mechanism is proposed to successfully model the silica-shell growth on the gold nanoparticles (NPs) and explain the formation of the ravine-structured surface of the Au@SiO 2 colloids. Furthermore, it is found that the ravine-structured surface strongly influences the formation of the Au@SiO 2 colloidal crystal films. The improved understanding of the surface morphology changes provides a suitable methodology for tailoring the growth of the core–shell structured colloids and assembling them into highly ordered colloidal crystal films.

In this manuscript, the synthesis and characterization of superparamagnetic particles and their silica-coated counterparts as building blocks for magnetic photonic crystals is fully described. The advantages and disadvantages of the presented synthetic method are discussed. Preliminary results considering the presence of magnetic species within a photonic crystal are also presented. Suppression of emission of the quantum dots within photonic crystals is attributed to a decrease of the number of available photonic modes for radiative decay. The presence of materials with permanent magnetic moments within photonic crystals shows that suppression of their emission is scaled with the strength of the magnetic field.

Following the impact of a single femtosecond light pulse on nickel nanostripes, material deformations—or “nanobumps”—are created. We have studied the dependence of these nanobumps on the length of nanostripes and verified the link with plasmons. More specifically, local electric currents can melt the nanostructures in the hotspots, where hydrodynamic processes give rise to nanobumps. This process is further confirmed by independently simulating local magnetic fields, since these are produced by the same local electric currents.

Building photonic crystals by combination of colloidal ordering and metal sputtering we were able to construct a system sensitive to an electrical field. In corresponding crystals we embedded the Dexter pair (Ir(ppy3) and BAlq) and investigated the influence of the band gap on the resonant energy transfer when the system is excited by light and by an electric field respectively. Our investigations extend applications of photonic crystals into the field of electroluminescence and LED technologies.

Photonic crystals have become an extremely active area of research, holding much potential for improvement and miniaturization of optical technology, just like semiconductors caused a revolution in electronics. A very popular sample to study in the visible region has been the synthetic opal, made by self-assembly processes from monodisperse dielectric spheres. Its high degree of symmetry and the nature of the dielectric materials usually employed do, however, limit its effectiveness in some ways. Here, we present an experimental investigation of modifications to these materials, adding enhanced magnetic interactions with the electromagnetic field and different shapes to the photonic crystal toolbox, as well as a combination of both.

Faraday rotation for magnetic field sensing can find applications in satellite altitude monitoring. Enhancing and tuning Faraday rotation is demonstrated in hybrid magnetic photonic crystals, based on an independent nanoscale engineering of two different materials (silica and iron oxide) at different length scales ( 200 nm). An engineering approach towards combined photonic band gap properties and magnetic functionalities, based on independent nanoscale engineering of two different materials at different length scales, is conceptually presented, backed by simulations, and experimentally confirmed. Large (> 200 nm) monodisperse nanospheres of transparent silica self-assemble into a photonic crystal with a visible band gap, which is retained upon infiltration of small (< 20 nm) nanoparticles of magnetic iron oxide. Enhancing and tuning Faraday rotation in photonic crystals is demonstrated.

We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge-transfer band localized at lambda = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state (+ZnP-AuP center dot) that displays a particularly long lifetime (tau=4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at lambda = 739 nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (beta = 2100 x 10(-30) esu at lambda = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.

12 pages, 11 figures, 9 tables.-- et al., A series of chromophoric salts has been prepared in which electron-rich 4-(dimethylamino)phenyl groups are connected via polyenyl chains to electron-accepting N-methylpyridinium or 3-methylbenzothiazolium units. These compounds have been characterized by using various techniques, including electronic absorption spectroscopy and cyclic voltammetry. Single-crystal X-ray structures have been determined for several salts, all of which crystallize centrosymmetrically. Molecular quadratic nonlinear optical (NLO) responses have been determined using femtosecond hyper-Rayleigh scattering (HRS) at 1300 and 800 nm and via Stark (electroabsorption) spectroscopic studies on the intense, visible π → π* intramolecular charge-transfer (ICT) bands. Large red shifts in the ICT transitions on replacing a pyridinium with a benzothiazolium unit indicate that the latter acts as a more effective electron acceptor. Both HRS and Stark measurements show that the static first hyperpolarizability β0 increases with polyene chain extension in both types of chromophore, and the benzothiazolium salts have larger NLO responses than their pyridinium analogues. The results of time-dependent density functional theory calculations using a polarizable solvent continuum model agree with the observation that β0 increases with chain lengthening, but the observed superiority of the benzothiazolium acceptor is not predicted either in the ICT energies or β0 values. Coupled perturbed Hartree−Fock and semiempirical INDO/S calculations similarly fail to reproduce this principal conclusion from the experimental studies., We thank the EPSRC for support (Grant GR/M93864) and the Fund for Scientific Research-Flanders (FWO-V, G.0297.04), the University of Leuven (GOA/2006/3), the Belgian Government (IUAP P5/3)), MCyT-FEDER (BQU2005-01368) and Gobierno de Aragon-Fondo Social Europeo (E39).