Nonlocal optical effects on the fluorescence and decay rates for admolecules at a metallic nanoparticle

Abstract

A phenomenological model is implemented to study the decay rates of fluorescing molecules in the vicinity of a metallic nanoparticle, wherein the nonlocal optical response of the particle is accounted for via the hydrodynamic model for the description of the free electrons in the metal. These nonlocal effects are examined for each of the radiative rate and the nonradiative rate of the admolecule, respectively. In addition, the overall fluorescence rate which includes the enhancement ratio for the driving field intensity is also studied. It is found that for particles of very small sizes (<10 nm), the nonlocal effects, in general, lead to significantly greater fluorescence rates and smaller nonradiative decay rates for the admolecules, with the effects on radiative rates depending crucially on the orientation of the molecules. Furthermore, the effects are mostly noticeable for molecules close to the metal particle and in processes where higher multipolar interactions are significant such as those in nonradiative decay processes. Above all, these nonlocal effects can still be observable in the presence of large surface damping imposed on the metallic electrons due to the ultrasmall sizes of these nanoparticles. The relevance of these effects to some of the latest experiments is discussed.

Two-fluid hydrodynamic model for semiconductors

“…The charge distribution for the LSP peak is also shown (marked with "Y"), and we see from the contour plot that although it is indeed a surface plasmon it also displays the pattern of a confined bulk plasmon. The reason is that the LSP resonance hybridizes with the b-fluid bulk plasmon marked by [2,4], resulting in a charge distribution with features from both surface and bulk plasmons. Such a hybridization would never take place in the HDM where the surface plasmons always are clearly separated in frequency from the bulk plasmons.…”

“…But when the sizes approach the nanoscale, the model is no longer able to explain experimentally observable phenomena like, for example, the blueshift of the resonance frequency of the localized surface plasmon (LSP) in metallic nanospheres [1]. An improved model that has been successful in describing the optical properties of metals on the nanoscale is the hydrodynamic Drude model (HDM) [2][3][4][5][6][7][8][9][10][11][12]. In this model, the polarization depends nonlocally on the electrical field, and the aforementioned blueshift appears as a size-dependent nonlocal effect [7,13,14].…”

Distance dependent quenching effect in nanoparticle dimers

“…The effect has been reported in the literature for a molecule placed in the vicinity of a planar surface, [11][12][13] a cavity, 14 a photonic crystal, 15,16 an optical probe, 17 and a nanoparticle. 18,19 This mechanism, usually referred to as molecular fluorescence [20][21][22] or the Purcell effect, 23 is meant to describe how the lifetime of a molecular excited state is not only a function of the molecule itself, but also of its surrounding environment. The lifetime is modified by both the radiative decay rate, due to photon emission, and the non-radiative decay rate, due to energy dissipation into the surrounding environment.…”

Van der Waals Forces Between Plasmonic Nanoparticles

“…We will also assume a local description of matter and use throughout the paper the Drude's dispersion law, ε (ω) = 1 − ω 2 pl ω(ω+i/τ ) , with ω pl = 15.8eV and (ω pl τ ) −1 = 0.04(Al). These assumptions are not very good for small enough nanoparticles (size less than 5 nm), where a nonlocal dielectric response of the nanoparticle (see [23]) and a radius-dependent imaginary part of the dielectric function (see, e.g., [24]) should be taken into account. So, our results can be used for nanoparticles in the range between 5 and 100 nm.…”