15 research outputs found
Anisotropic electrostatic screening of charged colloids in nematic solvents
The physical behaviour of anisotropic charged colloids is determined by their
material dielectric anisotropy, affecting colloidal self-assembly, biological
function and even out-of-equilibrium behaviour. However, little is known about
anisotropic electrostatic screening, which underlies all electrostatic
effective interactions in such soft or biological materials. In this work, we
demonstrate anisotropic electrostatic screening for charged colloidal particles
in a nematic electrolyte. We show that material anisotropy behaves markedly
different from particle anisotropy: The electrostatic potential and pair
interactions decay with an anisotropic Debye screening length, contrasting the
constant screening length for isotropic electrolytes. Charged dumpling-shaped
near-spherical colloidal particles in a nematic medium are used as an
experimental model system to explore the effects of anisotropic screening,
demonstrating competing anisotropic elastic and electrostatic effective pair
interactions for colloidal surface charges tunable from neutral to high,
yielding particle-separated metastable states. Generally, our work contributes
to the understanding of electrostatic screening in nematic anisotropic media.Comment: 15 pages, 5 figures, SM under ancillary file
Tuning and Switching a Plasmonic Quantum Dot Sandwich in a Nematic Line Defect
We study the quantum-mechanical effects arising in a single semiconductor
core/shell quantum dot controllably sandwiched between two plasmonic nanorods.
Control over the position and the sandwich confinement structure is achieved by
the use of a linear-trap, liquid-crystal line defect and laser tweezers that
push the sandwich together. This arrangement allows for the study of exciton
plasmon interactions in a single structure, unaltered by ensemble effects or
the complexity of dielectric interfaces. We demonstrate the effect of plasmonic
confinement on the photon-antibunching behavior of the quantum dot and its
luminescence lifetime. The quantum dot behaves as a single emitter when
nanorods are far away from the quantum dot but shows possible multiexciton
emission and a significantly decreased lifetime when tightly confined in a
plasmonic sandwich. These findings demonstrate that liquid crystal defects,
combined with laser tweezers, enable a versatile platform to study plasmonic
coupling phenomena in a nanoscale laboratory, where all elements can be
arranged almost at will.Comment: Supporting information at the en
Recommended from our members
Control of quantum dot emission by colloidal plasmonic pyramids in a liquid crystal
We study the plasmon-enhanced fluorescence of a single semiconducting quantum dot near the apex of a colloidal gold pyramid spatially localized by the elastic forces of the liquid crystal host. The gold pyramid particles were manipulated within the liquid crystal medium by laser tweezers, enabling the self-assembly of a semiconducting quantum dot dispersed in the medium near the apex of the gold pyramid, allowing us to probe the plasmon-exciton interactions. We demonstrate the effect of plasmon coupling on the fluorescence lifetime and the blinking properties of the quantum dot. Our results demonstrate that topological defects around colloidal particles in liquid crystal combined with laser tweezers provide a platform for plasmon exciton interaction studies and potentially could be extended to the scale of composite materials for nanophotonic applications.</p
Liquid Crystalline Order and Electric Switching of Upconversion Luminescence in Colloidal Nanorod Suspensions
International audienceThe polarizationâdependent photon upconversion luminescence properties of largeâscale orientationally ordered soft matter systems formed by colloidal nanorods dispersed in an isotropic solvent are studied. The electrostatically charged photonâupconverting nanorods form an isotropic dispersion at low concentrations, whereas orientational order and a nematic phase emerge at high concentrations. When an alternating electric field is applied, particles align in the direction of the electric field in both nematic and isotropic phases, though the nature of this electric switching is different in these two phases. Owing to the longârange orientational order in the nematic phase, the upconversion luminescence from the particles is polarized without an external field. Polarization dependence of these properties can also be electrically induced in an isotropic phase of the colloidal nanorods. Further, the dynamics of switching of photon upconversion luminescence in both nematic and isotropic dispersions are explored and their potential technological uses are dicussed
PlasmonâExciton Interactions Probed Using Spatial Coentrapment of Nanoparticles by Topological Singularities
We study plasmonâexciton interaction by using topological singularities to spatially confine, selectively deliver, cotrap and optically probe colloidal semiconductor and plasmonic nanoparticles. The interaction is monitored in a single quantum system in the bulk of a liquid crystal medium where nanoparticles are manipulated and nanoconfined far from dielectric interfaces using laser tweezers and topological configurations containing singularities. When quantum dot-in-a-rod particles are spatially colocated with a plasmonic gold nanoburst particle in a topological singularity core, its fluorescence increases because blinking is significantly suppressed and the radiative decay rate increases by nearly an order of magnitude owing to the Purcell effect. We argue that the blinking suppression is the result of the radiative rate change that mitigates Auger recombination and quantum dot ionization, consequently reducing nonradiative recombination. Our work demonstrates that topological singularities are an effective platform for studying and controlling plasmonâexciton interactions
Plasmon-Enhanced Energy Transfer for Improved Upconversion of Infrared Radiation in Doped-Lanthanide Nanocrystals
Upconversion of infrared radiation
into visible light has been
investigated for applications in photovoltaics and biological imaging.
However, low conversion efficiency due to small absorption cross-section
for infrared light (Yb<sup>3+</sup>), and slow rate of energy transfer
(to Er<sup>3+</sup> states) has prevented application of upconversion
photoluminescence (UPL) for diffuse sunlight or imaging tissue samples.
Here, we utilize resonant surface plasmon polaritons (SPP) waves to
enhance UPL in doped-lanthanide nanocrystals. Our analysis indicates
that SPP waves not only enhance the electromagnetic field, and hence
weak Purcell effect, but also increase the rate of resonant energy
transfer from Yb<sup>3+</sup> to Er<sup>3+</sup> ions by 6 fold. While
we do observe strong metal mediated quenching (14-fold) of green fluorescence
on flat metal surfaces, the nanostructured metal is resonant in the
infrared and hence enhances the nanocrystal UPL. This strong Coulombic effect on energy transfer can have
important implications for other fluorescent and excitonic systems
too