Stark Effect Control of the Scattering Properties of Plasmonic Nanogaps Containing an Organic Semiconductor

The development of actively tunable plas-monic nanostructures enables real-time reconfigurable and on demand enhancement of optical signals. This is an essential requirement for a wide range of applications such as sensing and nanophotonic devices, for which electrically driven tunability is required. By modifying the transition energies of a material via the application of an electric field, the Stark effect offers a reliable and practical approach to achieve such tunability. In this work, we report on the use of the Stark effect to control the scattering response of a plasmonic nanogap formed between a silver nanoparticle and an extended silver film separated by a thin layer of the organic semiconductor PQT-12. The plasmonic response of such nano-scattering sources follows the quadratic stark shift. Additionally, our approach allows to experimentally determine the polarizability of the semiconductor material embedded in the nanogap region, offering a new approach to probe the excitonic properties of extremely thin semi-conducting materials such as 2D materials under applied external electric field with nanoscale resolution

Plasmon-enhanced fluorescence in gold nanorod-quantum dot coupled systems

Plasmon-exciton coupling is of great importance to many optical devices and applications. One of the coupling manifestations is plasmon-enhanced fluorescence. Although this effect is demonstrated in numerous experimental and theoretical works, there are different particle shapes for which this effect is not fully investigated. In this work electrostatic complexes of gold nanorods and CdSe/CdZnS quantum dots were studied. Double-resonant gold nanorods have an advantage of the simultaneous enhancement of the absorption and emission when the plasmon bands match the excitation and fluorescence wavelengths of an emitter. A relationship between the concentration of quantum dots in the complexes and the enhancement factor was established. It was demonstrated that the enhancement factor is inversely proportional to the concentration of quantum dots. The maximal fluorescence enhancement by 10.8 times was observed in the complex with the smallest relative concentration of 2.5 quantum dots per rod and approximately 5 nm distance between them. Moreover, the influence of quantum dot location on the gold nanorod surface plays an important role. Theoretical study and experimental data indicate that only the position near the nanorod ends provides the enhancement. At the same time, the localization of quantum dots on the sides of the nanorods leads to the fluorescence quenching

Magnetic Mode Coupling in Hyperbolic Bowtie Meta-Antennas

Hyperbolic metaparticles have emerged as the next step in metamaterial applications, providing tunable electromagnetic properties on demand. However, coupling of optical modes in hyperbolic meta-antennas has not been explored. Here, we present in detail the magnetic and electric dipolar modes supported by a hyperbolic bowtie meta-antenna and clearly demonstrate the existence of two magnetic coupling regimes in such hyperbolic systems. The coupling nature is shown to depend on the interplay of the magnetic dipole moments, controlled by the meta-antenna effective permittivity and nanogap size. In parallel, the meta-antenna effective permittivity offers fine control over the electrical field spatial distribution. Our work highlights new coupling mechanisms between hyperbolic systems that have not been reported before, with a detailed study of the magnetic coupling nature, as a function of the structural parameters of the hyperbolic meta-antenna, which opens the route toward a range of applications from magnetic nanolight sources to chiral quantum optics and quantum interfaces

Impact of Surface Ligand on the Biocompatibility of InP/ZnS Quantum Dots with Platelets

InP/ZnS quantum dots (QDs) have received a large focus in recent years as a safer alternative to heavy metal-based QDs. Given their intrinsic fluorescent imaging capabilities, these QDs can be potentially relevant for in vivo platelet imaging. The InP/ZnS QDs are synthesized and their biocompatibility investigated through the use of different phase transfer agents. Analysis of platelet function indicates that platelet-QD interaction can occur at all concentrations and for all QD permutations tested. However, as the QD concentration increases, platelet aggregation is induced by QDs alone independent of natural platelet agonists. This study helps to define a range of concentrations and coatings (thioglycolic acid and penicillamine) that are biocompatible with platelet function. With this information, the platelet-QD interaction can be identified using multiple methods. Fluorescent lifetime imaging microscopy (FLIM) and confocal studies have shown QDs localize on the surface of the platelet toward the center while showing evidence of energy transfer within the QD population. It is believed that these findings are an important stepping point for the development of fluorescent probes for platelet imaging

Polarization switch between parallel and orthogonal collective resonances in aluminum arrays

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Optical characterisation of colloidal silver films on polypropylene

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Polarization switching between parallel and orthogonal collective resonances in arrays of metal nanoparticles

International audienceIn this work, we discuss excitation of orthogonal and parallel collective resonances in rectangular arrays of aluminum nanoparticles and switch between them with a change of array dimensions or polarization. We demonstrate that in the case of the substrate, scattered fields from nanoparticles can interact with each other in directions both parallel and orthogonal to the external electric field, which results in manifestation of the parallel coupling when localized plasmon resonance is near its spectral position. In this work, the parallel diffraction waves couple with in-plane quadrupolar mode excited with a scattered field coming from the neighboring nanoparticles. The rate of the parallel coupling depends on the interparticle distance, which allows us to control the intensity of the coupled mode

Possible nanoantenna control of chlorophyll dynamics for bioinspired photovoltaics

International audienceIn the context of using portions of a photosynthetic apparatus of green plants and photosynthesizing bacteria in bioinspired photovoltaic systems, we consider possible control of the chlorophyll excited state decay rate using nanoantennas in the form of a single metal and semiconductor nanoparticle. Since chlorophyll luminescence competes with electron delivery for chemical reactions chain and also to an external circuit, we examine possible excited state decay inhibition contrary to radiative rate enhancement. Both metal and semiconductor nanoparticles enable inhibition of radiative decay rate by one order of the magnitude as compared to that in vacuum, whereas a metal nanosphere cannot perform the overall decay inhibition since slowing down of radiative decay occurs only along with the similar growth of its nonradiative counterpart whereas a semiconductor nanoantenna is lossless. Additionally, at normal orientation of the emitter dipole moment to a nanoparticle surface, a silicon nanoparticle promotes enhancement of radiative decay by one order of the magnitude within the whole visible range. Our results can be used for other photochemical or photovoltaic processes, and strong radiative decay enhancement found for dielectric nanoantennas paves the way to radiative decays and light emitters engineering without non-radiative losses

Colloidal Silver Films on Polypropylene and Polyethylene

International audienceA simple procedure for the fabrication of colloidal silver films on the surface of flexible polymer substrates, such as polypropylene and polyethylene, with the use of only polyelectrolyte pre‐treatment is presented. The optical properties of these films depend on the number of predeposited polyelectrolyte layers and salt concentration. The uncharged nature of the polymer surface allows to alternate the first polyelectrolyte layer (positively or negatively charged). The proposed method of silver deposition can be used for manufacturing silver films of different density on the polymer surfaces. This approach is low‐cost, does not require special equipment and allows to control the surface properties of the films. Using an average salt concentration (0.5 M) during the deposition of polyelectrolytes allowed to produce the densest films