Photoluminescence of a Plasmonic Molecule

Abstract

Photoluminescent Au nanoparticles are appealing for biosensing and bioimaging applications because of their non-photobleaching and non-photoblinking emission. The mechanism of one-photon photoluminescence from plasmonic nanostructures is still heavily debated though. Here, we report on the one-photon photoluminescence of strongly coupled 50 nm Au nanosphere dimers, the simplest plasmonic molecule.We observe emission from coupled plasmonic modes as revealed by single-particle photoluminescence spectra in comparison to correlated dark-field scattering spectroscopy.The photoluminescence quantum yield of the dimers is found to be surprisingly similar to the constituent monomers, suggesting that the increased local electric field of the dimer plays a minor role, in contradiction to several proposed mechanisms. Aided by electromagnetic simulations of scattering and absorption spectra, we conclude that our data are instead consistent with a multistep mechanism that involves the emission due to radiative decay of surface plasmons generated from excited electronÀhole pairs following interband absorption.

Single-Particle Plasmon Voltammetry (spPV) for Detecting Anion Adsorption

“…51 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 stabilized 50 nm Au colloids (BBI Solutions) were washed with Millipore filtered deionized water and concentrated 10 times by centrifugation at 1400 rcf for 5 min. 200 µL of acetonitrile was added to the suspension and stirred for 30 min.…”

“…TEM analysis showed that the resulting solution contained 23% dimers with gap widths ranging from 1 to 5 nm. 51 Au Film Preparation: Semi-transparent conductive thin films were fabricated on clean glass coverslips by electron-beam evaporation of a 2 nm Ti adhesion layer followed by a 20 nm Au thin film. Film thickness was measured during deposition using a quartz crystal microbalance.…”

“…28-31, 36, 39-44 Also unlike the ITO substrate, anions readily adsorb to gold at anodic potentials [45][46][47] causing large changes in optical and electronic properties of the thin film. [48][49][50] Au nanoparticle monomers and chemically assembled dimers were deposited onto the two substrates, 51 and surface ligands were chemically removed from the monomers and dimers to leave the nanoparticles in electrical contact with the Figure 1. The potential-induced spectral shifts of Au plasmonic nanoparticles in Na 2 SO 4 electrolyte were strongly substrate-dependent.…”

Anticorrelation of Photoluminescence from Gold Nanoparticle Dimers with Hot-Spot Intensity

“…Decreasing the interparticle distance leads to a redshift of the scattering spectra and a correlated redshift of the PL spectra (Figure 3b). Nevertheless, the PL is slightly blueshifted with respect to the scattering spectrum 10,15,24,25,30 except for the closest distance. Most interestingly, the PL intensity is significantly decreased for decreasing distances d ; this is in contrast to the scattering intensity, which increases with decreasing d .…”

“…8 Further, it was recognized that a redshift of the scattering spectrum (due to gradual changes in geometry of gold nanostructures) is associated with a decrease of the PL intensity, while the scattering intensity increases 15,25,33 and while the absorption strength remains largely unchanged. 30 Only recently, it was pointed out by Lumdee et al 32 and Andersen et al 33 (following original ideas from Boyd et al 3 ) that the PL yield should follow the integral of the electric field squared inside the gold nanostructures as well as the gold-intrinsic d-hole recombination rate rather than scattering strengths or hot-spot intensities. However, their experiments were restricted to a single distance between a localized particle plasmon and a thin film surface plasmon.…”