Electronic structure and optical properties of metallic nanoshells

The electronic structure and optical properties of metallic nanoshells are investigated using a jellium model and the Time Dependent Local Density Approximation (TDLDA). An efficient numerical implementation enables applications to nanoshells of realistic size with up to a million electrons. We demonstrate how a frequency dependent background polarizability of the jellium shell can be included in the TDLDA formalism. The energies of the plasmon resonances are calculated for nanoshells of different sizes and with different dielectric cores, dielectric embedding media, and dielectric shell backgrounds. The plasmon energies are found to be in good agreement with the results from classical Mie scattering theory using a Drude dielectric function. A comparison with experimental data shows excellent agreement between theory and the measured frequency dependent absorption spectra

Gain assisted harmonic generation in near-zero permittivity metamaterials made of plasmonic nanoshells

We investigate enhanced harmonic generation processes in gain-assisted, near-zero permittivity metamaterials composed of spherical plasmonic nanoshells. We report the presence of narrow-band features in transmission, reflection and absorption induced by the presence of an active material inside the core of the nanoshells. The damping-compensation mechanism used to achieve the near-zero effective permittivity condition also induces a significant increase in field localization and strength and, consequently, enhancement of linear absorption. When only metal nonlinearities are considered, second and third harmonic generation efficiencies obtained by probing the structure in the vicinity of the near-zero permittivity condition approach values as high as for irradiance value as low as . These results clearly demonstrate that a relatively straightforward path now exists to the development of exotic and extreme nonlinear optical phenomena in the KW/cm2 rang

Spectroscopic properties of a two-level atom interacting with a complex spherical nanoshell

Frequency shifts, radiative decay rates, the Ohmic loss contribution to the nonradiative decay rates, fluorescence yields, and photobleaching of a two-level atom radiating anywhere inside or outside a complex spherical nanoshell, i.e. a stratified sphere consisting of alternating silica and gold concentric spherical shells, are studied. The changes in the spectroscopic properties of an atom interacting with complex nanoshells are significantly enhanced, often more than two orders of magnitude, compared to the same atom interacting with a homogeneous dielectric sphere. The detected fluorescence intensity can be enhanced by 5 or more orders of magnitude. The changes strongly depend on the nanoshell parameters and the atom position. When an atom approaches a metal shell, decay rates are strongly enhanced yet fluorescence exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss contribution to the nonradiative decay rates for an atomic dipole within the silica core of larger nanoshells may be decreasing when the silica core - inner gold shell interface is approached. The quasistatic result that the radial frequency shift in a close proximity of a spherical shell interface is approximately twice as large as the tangential frequency shift appears to apply also for complex nanoshells. Significantly modified spectroscopic properties (see computer program (pending publication of this manuscript) freely available at http://www.wave-scattering.com) can be observed in a broad band comprising all (nonresonant) optical and near-infrared wavelengths.Comment: 20 pages plus 63 references and 11 figures, plain LaTex, for more information see http://www.wave-scattering.com (color of D sphere in figures 2-6 altered, minor typos corrected.

Multilayered plasmonic nanostructures for solar energy harvesting

Optical properties of core-shell-shell Au@SiO2@Au nanostructures and their solar energy harvesting applications are theoretically investigated using Mie theory and heat transfer equations. The theoretical analysis associated with size-dependent modification of the bulk gold dielectric function agrees well with previous experimental results. We use the appropriate absorption cross-section to determine the solar energy absorption efficiency of the nano-heterostructures, which is strongly structure-dependent, and to predict the time-dependent temperature increase of the nanoshell solution under simulated solar irradiation. Comparisons to prior temperature measurements and theoretical evaluation of the solar power conversion efficiency are discussed to provide new insights into underlying mechanisms. Our approach would accelerate materials and structure testing in solar energy harvesting.Comment: 6 figures, 6 pages, Just accepted in Journal of Physical Chemistry

How toxic are gold nanoparticles? The state-of-the-art.

With the growing interest in biotechnological applications of gold nanoparticles and their effects exerted on the body, the possible toxicity is becoming an increasingly important issue. Numerous investigations carried out, in the last few years, under different experimental conditions, following different protocols, have produced in part conflicting results which have leaded to different views about the effective gold nanoparticle safety in human applications. This work is intended to provide an overview on the most recent experimental results in order to summarize the current state-of-the-art. However, rather than to present a comprehensive review of the available literature in this field, that, among other things, is really huge, we have selected some representative examples of both in vivo and in vitro investigations, with the aim of offering a scenario from which clearly emerges the need of an urgent and impelling standardization of the experimental protocols. To date, despite the great potential, the safety of gold nanoparticles is highly controversial and important concerns have been raised with the need to be properly addressed. Factors such as shape, size, surface charge, surface coating and surface functionalization are expected to influence interactions with biological systems at different extents, with different outcomes, as far as gold nanoparticle potentiality in biomedical applications is concerned. Moreover, despite the continuous attempt to establish a correlation between structure and interactions with biological systems, we are still far from assessing the toxicological profile of gold nanoparticles in an unquestionable manner. This review is intended to provide a contribution in this direction, offering some suggestions in order to reach the systematization of data over the most relevant physico-chemical parameters, which govern and control toxicity, at different cellular and organismal levels

Enhancement of perovskite solar cells by plasmonic nanoparticles

Synthetic perovskites with photovoltaic properties open a new era in solar photovoltaics. Due to high optical absorption perovskite-based thin-film solar cells are usually considered as fully absorbing solar radiation on condition of ideal blooming. However, is it really so? The analysis of the literature data has shown that the absorbance of all photovoltaic pervoskites has the spectral hole at infrared frequencies where the solar radiation spectrum has a small local peak. This absorption dip results in the decrease of the optical efficiency of thin-film pervoskite solar cells by nearly 3% and close the ways of utilise them at this range for any other applications. In our work we show that to cure this shortage is possible complementing the basic structure by an inexpensive plasmonic array.Comment: 6 pages 6 picture