Marinella Striccoli

Optical properties of hybrid composites based on highly luminescent CdS nanocrystals in polymer

High quality luminescent CdS nanocrystals (NCs), with band edge emission tunable in the blue region of the visible spectrum, were synthesized by means of thermal decomposition of precursors with oleic acid as the surfactant and incorporated in optically transparent polystyrene (PS) and poly(methyl methacrylate) (PMMA). The optical properties of the obtained nanocomposite films were investigated by absorption and emission spectroscopies. Enhancement of the band edge luminescence of CdS quantum dots was observed in both polymer matrices and the fluorescence of the composites retained narrow emission profiles. Capping exchange at the NC surface with octylamine, demonstrated to improve the luminescence properties in solution, was performed in order to investigate the role played by surface ligands in the nanocomposite. Octylamine capped NCs immobilized in the polymers showed high defect state emission and visible quenching of band edge luminescence, indicating an effective interaction between oleic acid and PMMA and PS polymeric chains.

Dispersed and encapsulated gain medium in plasmonic nanoparticles: a multipronged approach to mitigate optical losses.

The performance of all metamaterial-based applications is significantly limited by the inherent and strong energy dissipation present in metals, especially in the visible range. In fact, these materials suffer from rather strong damping of the plasmon fields which can become obstructive for most optical and photonic applications. Therefore, eliminating losses in optical metamaterials is critical for enabling their numerous potential applications. We experimentally demonstrate that the incorporation of gain material (fluorophores) in the high-local-field areas of a metamaterial subunits (gold core/silica shell nanoparticles) makes it possible to induce resonant energy transfer processes from gain units to plasmonic nanoparticles. A comparison between gain-assisted (nanoparticle-dye dispersion) and gain-functionalized (dye encapsulated into the shell) systems is reported. Fluorescence quenching and time-resolved spectroscopy along with modification of Rayleigh scattering and transmission of a probe beam as a function of impinging energy are key evidence of the strong coupling occurring between NPs and gain medium. The multipronged approach used to compensate losses in these metal-based subunits permits one to obtain important advances in materials science and paves the way toward further promising scientific research aimed to enable the wide range of electromagnetic properties of optical metamaterials.

TiO2 nanorods/PMMA copolymer-based nanocomposites: highly homogeneous linear and nonlinear optical material

Original nanocomposites have been obtained by direct incorporation of pre-synthesized oleic acid capped TiO(2) nanorods into properly functionalized poly(methyl methacrylate) copolymers, carrying carboxylic acid groups on the repeating polymer unit. The presence of carboxylic groups on the alkyl chain of the host functionalized copolymer allows an highly homogeneous dispersion of the nanorods in the organic matrix. The prepared TiO(2)/PMMA-co-MA nanocomposites show high optical transparency in the visible region, even at high TiO(2) nanorod content, and tunable linear refractive index depending on the nanoparticle concentration. Finally measurements of nonlinear optical properties of TiO(2) polymer nanocomposites demonstrate a negligible two-photon absorption and a negative value of nonlinear refractive index, highlighting the potential of the nanocomposite for efficient optical devices operating in the visible region.

Spectroscopic study on imidazolium-based ionic liquids: effect of alkyl chain length and anion.

Room temperature ionic liquids are currently used as functional materials in several application and their optical investigation can provide a better understanding of their physical and chemical behavior. Absorption and emission properties of imidazolium-based ILs have been attributed to the imidazolium moiety and related to the presence of energetically different aggregates. Here, time-integrated and time-resolved investigation has been carried out on 1-alkyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids with different chain lengths in order to probe the occurrence of energy transfer processes, and hence to disclose the presence of various states with different energy. Such a study contributes to provide relevant insight on the effect of alkyl chain and anion type on the emission characteristics, and, hence, on the presence of associated structures.

High quality CdS nanocrystals: surface effects

Stable and highly luminescent CdS nanocrystals (NCs) have been synthesized by means of decomposition of suitable precursors (CdO and elemental sulphur) in octadecene (ODE) and oleic acid at high temperature. Absorption and steady state photoluminescence (PL) measurements have been carried out to study the intrinsic properties of nanocrystals and the effect of ligand and solvent on emission properties. Ageing of nanocrystals has been investigated, and an efficient mechanism of emission recovery has been identified, showing the active role of non coordinating solvent and oleic acid in modifying the surface states.

Colloidal Inorganic Nanocrystal Based Nanocomposites: Functional Materials for Micro and Nanofabrication

The unique size- and shape-dependent electronic properties of nanocrystals (NCs) make them extremely attractive as novel structural building blocks for constructing a new generation of innovative materials and solid-state devices. Recent advances in material chemistry has allowed the synthesis of colloidal NCs with a wide range of compositions, with a precise control on size, shape and uniformity as well as specific surface chemistry. By incorporating such nanostructures in polymers, mesoscopic materials can be achieved and their properties engineered by choosing NCs differing in size and/or composition, properly tuning the interaction between NCs and surrounding environment. In this contribution, different approaches will be presented as effective opportunities for conveying colloidal NC properties to nanocomposite materials for micro and nanofabrication. Patterning of such nanocomposites either by conventional lithographic techniques and emerging patterning tools, such as ink jet printing and nanoimprint lithography, will be illustrated, pointing out their technological impact on developing new optoelectronic and sensing devices.

Inkjet‐Printed Multicolor Arrays of Highly Luminescent Nanocrystal‐Based Nanocomposites

Inkjet technology is a compelling method for the flexible and cost-effective printing of functional inks. We show that nanocomposite solutions based on polystyrene and differently sized core/shell-type nanocrystals (NCs) formed by a CdSe core coated with a shell of ZnS (CdSe@ZnS) in a single solvent, chloroform, can be reliably dispensed into luminescent, multicolor pixel arrays. This study demonstrates the relevance of parameters like polymer concentration and nozzle diameter, highlighting how the optimal conditions to print NCs embedded in 5 wt% polystyrene nanocomposite are given by a 70-microm-diameter nozzle. The obtained structures show that the bright size-dependent emission of the NCs in the nanocomposite is retained in the printed pixels.

Spontaneous emission control of colloidal nanocrystals using nanoimprinted photonic crystals

The authors report on the fabrication and optical characterizations of two-dimensional photonic crystals fabricated by nanoimprint lithography in a nanocomposite polymer incorporating highly luminescent and red emitting (CdSe)ZnS core-shell colloidal nanocrystals. Photonic crystal structures enhance the light emitted from the quantum sized nanoparticles in the composite layer by slowing the propagation speed of the photons, thus increasing the coupling to the out-of-plane radiative modes. A 200% enhancement of the light collection is achieved compared to an unpatterned sample.

Biofunctionalization of anisotropic nanocrystalline semiconductor-magnetic heterostructures.

Asymmetric binary nanocrystals (BNCs) formed by a spherical γ-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications.

Luminescent nanocrystals in phospholipid micelles for bioconjugation : An optical and structural investigation

Organic capped luminescent CdSe@ZnS nanocrystals (NCs) have been incorporated in block copolymer micelles, formed by polyethylene glycol modified phospholipids (PEG lipids). The obtained water soluble NC including PEG lipid micelles have been conjugated with bovine serum albumine (BSA). The entire process has been investigated by using optical, structural and electrophoretic complementary techniques. Such an integrated approach has allowed to elucidate critical issues, such as the time and temperature effects on the phase behavior of the PEG lipid/NC aggregate structures, the emitting properties of the NCs before and after micelle formation and bio-conjugation and the effect of conjugation on the biological moiety. The overall results provide relevant insight on the fabrication of the bio-conjugates, on their stability and on preparative procedure reproducibility, in view of the use of the resulting protein decorated NCs as multifunctional hybrid building blocks for the fabrication of a variety of supramolecular assemblies to exploit in biological sensing and diagnostic applications.