Strong luminescence quantum-efficiency enhancement near prolate metal nanoparticles: Dipolar versus higher-order modes

Abstract

We present a theoretical study of the radiative and nonradiative decay rates of an optical emitter in close proximity to a prolate-shaped metal nanoparticle. We use the model developed by Gersten and Nitzan, that we correct for radiative reaction and dynamic depolarization and extend for prolate particle shapes. We show that prolateshaped metal nanoparticles can lead to much higher quantum efficiency enhancements than corresponding spherical nanoparticles. For properly engineered emitter-nanoparticle geometries, quantum efficiency enhancements from an initial value of 1% (in absence of the nanoparticle) to 70% are feasible. We describe the anisotropy-induced enhancement effects in terms of large field enhancements near the metal tips that cause strong coupling to the (radiative) dipolar modes. For increasing particle anisotropy, a strong spectral separation between radiative dipolar and dark higher-order modes occurs, which leads to higher radiative efficiencies for anisotropic particles. In addition, we demonstrate that for large (> 100 nm) nanoparticles, the influence of Ohmic losses on plasmon-enhanced * Electronic address: polman@amolf.nl 1 luminescence is substantially reduced, which implies that, if prolate shaped, even lossy metals such as Al and Cu are suitable materials for optical nano-antennas.2

Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods

“…11,12 This phenomenon, which can be seen as a Förster energy transfer process, can also be explained by coupling to higher order dark modes, which decay faster than the dipolar mode. 12, 13 Fluorescence enhancement by plasmonic nanoparticles has been studied extensively over the past few decades. Early reports by the groups of Sandoghdar 14 and Novotny 15 employed a single gold nanosphere of 80 nm in diameter and achieved a fluorescence enhancement of a factor of 9.…”

Accelerated single photon emission from dye molecule-driven nanoantennas assembled on DNA

“…These modes do not radiate efficiently and are described as dark, while the dipolar resonances of nanoantennas are bright as they couple readily to the far-field. Because of overlapping dipolar and multipolar resonances and weak field confinement, spherical silver or gold particles are not efficient antennas 4 but they can be controllably coupled to single molecules (SMs) using atomic force microscopy 5,6 . Elongated particles and particle pairs with nanometre gaps have been proposed as more efficient antennas because they offer larger confinements and a bright longitudinal mode red-shifted with respect to lossy high-energy modes 4,7 .…”

Directional emission from a single plasmonic scatterer

“…For larger sizes higher-order multipole contributions become significant. The coupling efficiency to different moments strongly depends on the type of excitation 43,44 , particle shape and dielectric environment. In particular for cases where the particles have a non-spherical shape and/or are placed in an asymmetric dielectric environment like on a substrate, quantifying the contributions of the different multipoles is complex.…”