Efficient energy transfer in layered hybrid organic/inorganic nanocomposites: A dual function of semiconductor nanocrystals

The efficiency of energy transfer in hybrid organic/inorganic nanocomposites based on conjugated polymers and semiconductor nanocrystals is strongly dependent on both the energy transfer rate and the rate of the nonradiative recombination of the polymer. We demonstrate that the polymer nonradiative recombination can be reduced by the suppression of exciton diffusion via proper morphology engineering of a hybrid structure. In the layer-by-layer assembled nanocomposite of a conjugated polymer and CdTe nanocrystals the latter have a dual role: first, they are efficient exciton acceptors and, second, they reduce nonradiative recombination in the polymer by suppressing exciton diffusion across the layers.Fil: Lutich, Andrey A.. Ludwig Maximilians Universitat; AlemaniaFil: Pöschl, Andreas. Ludwig Maximilians Universitat; AlemaniaFil: Jiang, Guoxin. Ludwig Maximilians Universitat; AlemaniaFil: Stefani, Fernando Daniel. Ludwig Maximilians Universitat; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Susha, Andrei S.. City University of Hong Kong; ChinaFil: Rogach, Andrey L.. City University of Hong Kong; ChinaFil: Feldmann, Jochen. Ludwig Maximilians Universitat; Alemani

Optical trapping and manipulation of plasmonic nanoparticles: fundamentals, applications, and perspectives

This feature article discusses the optical trapping and manipulation of plasmonic nanoparticles, an area of current interest with potential applications in nanofabrication, sensing, analytics, biology and medicine. We give an overview over the basic theoretical concepts relating to optical forces, plasmon resonances and plasmonic heating. We discuss fundamental studies of plasmonic particles in optical traps and the temperature profiles around them. We place a particular emphasis on our own work employing optically trapped plasmonic nanoparticles towards nanofabrication, manipulation of biomimetic objects and sensing

Inorganic–organic nanocomposites of CdSe nanocrystals surface-modified with oligo- and poly(fluorene) moieties

We report a facile grafting-from strategy towards the synthesis of inorganic–organic composites of semiconductor nanocrystals and wide-bandgap polymers. Amino-functional fluorenes have been used as co-ligands for CdSe nanocrystals, thus enabling us to design their surface directly during the synthesis. Highly monodisperse, strongly emitting CdSe nanocrystals have been obtained. Subsequently, a straightforward Yamamoto C–C coupling protocol was used to carry out surface polymerisation, hence modifying CdSe nanocrystals with oligo- and poly(fluorene) moieties. Both amino-fluorene capped CdSe nanocrystals and the resulting nanocrystal–polymer composites were characterized in detail by optical and FT-IR spectroscopy, TEM, AFM, and gel permeation chromatography, showing their potential as novel functional inorganic–organic hybrid materials

Laser printing single gold nanoparticles

Current colloidal synthesis is able to produce an extensive spectrum of nanoparticles with unique optoelectronic, magnetic, and catalytic properties. In order to exploit them in nanoscale devices, flexible methods are needed for the controlled integration of nanoparticles on surfaces with few-nanometer precision. Current technologies usually involve a combination of molecular self-assembly with surface patterning by diverse lithographic methods like UV, dip-pen, or microcontact printing.1,2 Here we demonstrate the direct laser printing of individual colloidal nanoparticles by using optical forces for positioning and the van der Waals attraction for binding them to the substrate. As a proof-of-concept, we print single spherical gold nanoparticles with a positioning precision of 50 nm. By analyzing the printing mechanism, we identify the key physical parameters controlling the method, which has the potential for the production of nanoscale devices and circuits with distinct nanoparticles.Fil: Urban, Alexander S.. Ludwig Maximilians Universitat; AlemaniaFil: Lutich, Andrey A.. Ludwig Maximilians Universitat; AlemaniaFil: Stefani, Fernando Daniel. Ludwig Maximilians Universitat; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Feldmann, Jochen. Ludwig Maximilians Universitat; Alemani

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We report on anisotropic light scattering in nanoporous anodic alumina. Light coming at various angles with respect to the pore axis was found to be scattered predominantly in the solid angle adjacent to the pore axis. Such scattering indicatrix we explain in the terms of redistributed local density of photon states in irregular nanostructured materials. In the case of porous alumina local density of photon states and light scattering probability are increased in the direction of the pore axis. We demonstrate by the example of PAA that nanostructured aperiodic materials can possess birefringent properties. We demonstrate and explain formation of the scattering rings by transmitted laser light in birefringent nanoporous anodic alumina.</p

Optical Force Stamping Lithography

Here we introduce a new paradigm of far-field optical lithography, <i>optical force stamping lithography</i>. The approach employs optical forces exerted by a spatially modulated light field on colloidal nanoparticles to rapidly stamp large arbitrary patterns comprised of single nanoparticles onto a substrate with a single-nanoparticle positioning accuracy well beyond the diffraction limit. Because the process is all-optical, the stamping pattern can be changed almost instantly and there is no constraint on the type of nanoparticle or substrates used

Anisotropic light scattering in nanoporous materials:A photon density of states effect

Similar to spontaneous emission of photons and inelastic (Raman) scattering, elastic (Rayleigh) scattering of light is controlled by spectral and spatial distribution of photon density of states, DOS (density of electromagnetic modes). However, to date Rayleigh scattering in nanoporous media has not become the subject of discussion in the context of photon DOS effects. In this paper, we consider light scattering in porous materials in the context of spectral, spatial, and angular redistribution of photon DOS in materials with pores whose size and spacing are of the order of light wavelength. The DOS effect results in predictable and controllable modification of scattering and can be purposefully used in certain light harvesting and illumination systems. A possible role of the effect in the cornea of eye is outlined for seeing at grazing incidence of light beams with respect to an eye pupil.</p

Comparative optical study of colloidal anatase titania nanorods and atomically thin wires

We present results of a comparative study of colloidal anatase titanium oxide nanorods and extremely thin atomic wires of systematically decreasing (2.6 nm down to 0.5 nm) diameter in terms of their optical absorption as well as steady-state and time-resolved photoluminescence. Steady-state photoluminescence spectra of the titania samples show three well-distinguished spectral components, which are ascribed to excitonic emission (4.26 +/- 0.2 eV), as well as radiative recombination of trapped holes with electrons from the conduction band (4.04 +/- 0.4 eV) and radiative recombination of trapped electrons with holes in the valence band (3.50 +/- 0.2 eV) in nanocrystalline anatase TiO2. Time-resolved photoluminescence measurements point out the existence of different emissive species responsible for the appearance of high-energetic and low-energetic emission peaks of TiO2 atomic wires and nanorods