116 research outputs found
Modal Coupling of Single Photon Emitters Within Nanofiber Waveguides
Nanoscale generation of individual photons in confined geometries is an
exciting research field aiming at exploiting localized electromagnetic fields
for light manipulation. One of the outstanding challenges of photonic systems
combining emitters with nanostructured media is the selective channelling of
photons emitted by embedded sources into specific optical modes and their
transport at distant locations in integrated systems. Here, we show that
soft-matter nanofibers, electrospun with embedded emitters, combine
subwavelength field localization and large broadband near-field coupling with
low propagation losses. By momentum spectroscopy, we quantify the modal
coupling efficiency identifying the regime of single-mode coupling. These
nanofibers do not rely on resonant interactions, making them ideal for
room-temperature operation, and offer a scalable platform for future quantum
information technology
The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibers
Polymer fibers are currently exploited in tremendously important
technologies. Their innovative properties are mainly determined by the behavior
of the polymer macromolecules under the elongation induced by external
mechanical or electrostatic forces, characterizing the fiber drawing process.
Although enhanced physical properties were observed in polymer fibers produced
under strong stretching conditions, studies of the process-induced nanoscale
organization of the polymer molecules are not available, and most of fiber
properties are still obtained on an empirical basis. Here we reveal the
orientational properties of semiflexible polymers in electrospun nanofibers,
which allow the polarization properties of active fibers to be finely
controlled. Modeling and simulations of the conformational evolution of the
polymer chains during electrostatic elongation of semidilute solutions
demonstrate that the molecules stretch almost fully within less than 1 mm from
jet start, increasing polymer axial orientation at the jet center. The
nanoscale mapping of the local dichroism of individual fibers by polarized
near-field optical microscopy unveils for the first time the presence of an
internal spatial variation of the molecular order, namely the presence of a
core with axially aligned molecules and a sheath with almost radially oriented
molecules. These results allow important and specific fiber properties to be
manipulated and tailored, as here demonstrated for the polarization of emitted
light.Comment: 45 pages, 10 figures, Macromolecules (2014
Nanowire-Intensified MEF in Hybrid Polymer-Plasmonic Electrospun Filaments
Hybrid polymer-plasmonic nanostructures might combine high enhancement of
localized fields from metal nanoparticles with light confinement and long-range
transport in subwavelength dielectric structures. Here we report on the complex
behavior of fluorophores coupling to Au nanoparticles within polymer nanowires,
which features localized metal-enhanced fluorescence (MEF) with unique
characteristics compared to conventional structures. The intensification effect
when the particle is placed in the organic filaments is remarkably higher with
respect to thin films of comparable thickness, thus highlighting a specific,
nanowire-related enhancement of MEF effects. A dependence on the confinement
volume in the dielectric nanowire is also evidenced, with MEF significantly
increasing upon reducing the wire diameter. These findings are rationalized by
finite element simulations, predicting a position-dependent enhancement of the
quantum yield of fluorophores embedded in the fibers. Calculation of the
ensemble-averaged fluorescence enhancement unveils the possibility of strongly
enhancing the overall emission intensity for structures with size twice the
diameter of the embedded metal particles. These new, hybrid fluorescent systems
with localized enhanced emission, as well as the general Nanowire-Intensified
MEF effect associated to them, are highly relevant for developing nanoscale
light-emitting devices with high efficiency and inter-coupled through nanofiber
networks, highly sensitive optical sensors, and novel laser architectures.Comment: 29 pages, 12 figures, Small (2018
Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers
Conjugated polymers are complex multi-chromophore systems, with emission
properties strongly dependent on the electronic energy transfer through active
sub-units. Although the packing of the conjugated chains in the solid state is
known to be a key factor to tailor the electronic energy transfer and the
resulting optical properties, most of the current solution-based processing
methods do not allow for effectively controlling the molecular order, thus
making the full unveiling of energy transfer mechanisms very complex. Here we
report on conjugated polymer fibers with tailored internal molecular order,
leading to a significant enhancement of the emission quantum yield. Steady
state and femtosecond time-resolved polarized spectroscopies evidence that
excitation is directed toward those chromophores oriented along the fiber axis,
on a typical timescale of picoseconds. These aligned and more extended
chromophores, resulting from the high stretching rate and electric field
applied during the fiber spinning process, lead to improved emission
properties. Conjugated polymer fibers are relevant to develop optoelectronic
plastic devices with enhanced and anisotropic properties.Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical
Society, (2016
Nanoparticle-doped electrospun fiber random lasers with spatially extended light modes
Complex assemblies of light-emitting polymer nanofibers with molecular
materials exhibiting optical gain can lead to important advance to amorphous
photonics and to random laser science and devices. In disordered mats of
nanofibers, multiple scattering and waveguiding might interplay to determine
localization or spreading of optical modes as well as correlation effects. Here
we study electrospun fibers embedding a lasing fluorene-carbazole-fluorene
molecule and doped with titania nanoparticles, which exhibit random lasing with
sub-nm spectral width and threshold of about 9 mJ cm^-2 for the absorbed
excitation fluence. We focus on the spatial and spectral behavior of optical
modes in the disordered and non-woven networks, finding evidence for the
presence of modes with very large spatial extent, up to the 100
micrometer-scale. These findings suggest emission coupling into integrated
nanofiber transmission channels as effective mechanism for enhancing spectral
selectivity in random lasers and correlations of light modes in the complex and
disordered material.Comment: 22 pages, 6 figure
Diverse regimes of mode intensity correlation in nanofiber random lasers through nanoparticle doping
Random lasers are based on disordered materials with optical gain. These
devices can exhibit either intensity or resonant feedback, relying on diffusive
or interference behaviour of light, respectively, which leads to either
coupling or independent operation of lasing modes. We study for the first time
these regimes in complex, solid-state nanostructured materials. The number of
lasing modes and their intensity correlation features are found to be
tailorable in random lasers made of light-emitting, electrospun polymer fibers
upon nanoparticle doping. By material engineering, directional waveguiding
along the length of fibers is found to be relevant to enhance mode correlation
in both intensity feedback and resonant feedback random lasing. The here
reported findings can be used to establish new design rules for tuning the
emission of nano-lasers and correlation properties by means of the
compositional and morphological properties of complex nanostructured materials.Comment: 30 pages, 10 figure
Bright light emission and waveguiding in conjugated polymer nanofibers electrospun from organic-salt added solutions
Light emitting electrospun nanofibers of
poly-[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N'-diphenyl)-N,N'-di(p-butyl-oxy-phenyl)-1,4-diaminobenzene)]
(PFO-PBAB) are produced by electrospinning under different experimental
conditions. In particular, uniform fibers with average diameter of 180 nm are
obtained by adding an organic salt to the electrospinning solution. The
spectroscopic investigation assesses that the presence of the organic salt does
not alter the optical properties of the active material, therefore providing an
alternative approach for the fabrication of highly emissive conjugated polymer
nanofibers. The produced nanofibers display self-waveguiding of light, and
polarized photoluminescence, which is especially promising for embedding active
electrospun fibers in sensing and nanophotonic devices.Comment: 31 pages, 9 figures, 1 table. Macromolecules (2013
Electrospun Conjugated Polymer/Fullerene Hybrid Fibers: Photoactive Blends, Conductivity through Tunnelling-AFM, Light-Scattering, and Perspective for Their Use in Bulk-Heterojunction Organic Solar Cells
Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are
prepared by electrospinning, and their properties assessed by scanning
electron, atomic and lateral force, tunnelling, and confocal microscopy, as
well as by attenuated total reflection Fourier transform-infrared spectroscopy,
photoluminescence quantum yield and spatially-resolved fluorescence.
Highlighted features include ribbon-shape of the realized fibers, and the
persistence of a network serving as a template for heterogeneous active layers
in solar cell devices. A set of favorable characteristics is evidenced in this
way in terms of homogeneous charge transport behavior and formation of
effective interfaces for diffusion and dissociation of photogenerated excitons.
The interaction of the organic filaments with light, exhibiting specific
light-scattering properties of the nanofibrous mat, might also contribute to
spreading incident radiation across the active layers, thus potentially
enhancing photovoltaic performance. This method might be applied to other
electron donor-electron acceptor material systems for the fabrication of solar
cell devices enhanced by nanofibrillar morphologies embedding conjugated
polymers and fullerene compounds.Comment: 35 pages, 9 figure
Sub-ms dynamics of the instability onset of electrospinning
Electrospun polymer jets are imaged for the first time at an ultra-high rate
of 10,000 frames per second, investigating the process dynamics, and the
instability propagation velocity and displacement in space. The polymer
concentration, applied voltage bias and needle-collector distance are
systematically varied, and their influence on the instability propagation
velocity and on the jet angular fluctuations analyzed. This allows us to unveil
the instability formation and cycling behavior, and its exponential growth at
the onset, exhibiting radial growth rates of the order of 10^3 s^-1. Allowing
the conformation and evolution of polymeric solutions to be studied in depth,
high-speed imaging at sub-ms scale shows a significant potential for improving
the fundamental knowledge of electrified jets, leading to obtain finely
controllable bending and solution stretching in electrospinning, and
consequently better designed nanofibers morphologies and structures.Comment: 23 pages, 9 figure
Identification of two novel LDLR variants by Next Generation Sequencing
Introduction. Familial hypercholesterolemia (FH) is an autosomal dominant inherited disease characterized by elevated plasma low-density lipoprotein cholesterol (LDL-C). Targeted Next Generation Sequencing (NGS) is a new opportunity to expand the existing pathogenic variants (PVs) spectrum associated to FH. Our aim was to report a diagnostic NGS-based approach to detect variants associated to FH.Methods. We report two patients: a 48-year-old Asian woman, without known history of hypercholesterolemia and a 46-year-old Caucasian man, with childhood hypercholesterolemia.Results. An effective NGS-based pipeline, FH-Devyser kit/Amplicon Suite, beginning from sequencing to data analysis, did not identify known PVs in the LDLR, APOB, APOE, LDLRAP1, STAP1 and PCSK9 genes, but revealed two novel LDLR variants (c.1564A>T, p.Ile522Phe and c.1688C>T, p.Pro563Leu).Discussion and conclusions. This study showed that an effective NGS-based pipeline led to a definitive diagnosis in two FH families, allowing to plan their therapeutic treatment. Although the functional consequence of the two LDLR variants needs to be assessed in vitro, the in silico analysis and high preservation of the two amino acid positions observed in the LDLR protein, across different animal species, suggest that both variants are deleterious
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