11 research outputs found
Spatial imaging of modifications to fluorescence lifetime and intensity by individual Ag nanoparticles
Highly ordered periodic arrays of silver nanoparticles have been fabricated
which exhibit surface plasmon resonances in the visible spectrum. We
demonstrate the ability of these structures to alter the fluorescence
properties of vicinal dye molecules by providing an additional radiative decay
channel. Using fluorescence lifetime imaging microscopy (FLIM), we have created
high resolution spatial maps of the molecular lifetime components; these show
an order of magnitude increase in decay rate from a localized volume around the
nanoparticles, resulting in a commensurate enhancement in the fluorescence
emission intensity.Comment: 3 pages, 2 figures, submitted Applied Physics Letter
Plasmonic engineering of metal nanoparticles for enhanced fluorescence and Raman scattering
We have investigated the effects of tuning the localized surface plasmon
resonances (LSPRs) of silver nanoparticles on the fluorescence intensity,
lifetime, and Raman signal from nearby fluorophores. The presence of a metallic
structure can alter the optical properties of a molecule by increasing the
excitation field, and by modifying radiative and non-radiative decay
mechanisms. By careful choice of experimental parameters we have been able to
decouple these effects. We observe a four-fold increase in fluorescence
enhancement and an almost 30-fold increase in decay rate from arrays of Ag
nanoparticles, when the LSPR is tuned to the emission wavelength of a locally
situated fluorophore. This is consistent with a greatly increased efficiency
for energy transfer from fluorescence to surface plasmons. Additionally,
surface enhanced Raman scattering (SERS) measurements show a maximum
enhancement occurs when both the incident laser light and the Raman signal are
near resonance with the plasmon energy. Spatial mapping of the SERS signal from
a nanoparticle array reveals highly localized differences in the excitation
field resulting from small differences in the LSPR energy.Comment: Submitted to Plasmonics (Springer
Strong coupling of localized plasmons and molecular excitons in nanostructured silver films
We report on the resonant coupling between localized surface plasmon
resonances (LSPRs) in nanostructured Ag films, and an adsorbed monolayer of
Rhodamine 6G dye. Hybridization of the plasmons and molecular excitons creates
new coupled polaritonic modes, which have been tuned by varying the LSPR
wavelength. The resulting polariton dispersion curve shows an anticrossing
behavior which is very well fit by a simple coupled-oscillator Hamiltonian,
giving a giant Rabi-splitting energy of ~400 meV. The strength of this coupling
is shown to be proportional to the square root of the molecular density. The
Raman spectra of R6G on these films show an enhancement of many orders of
magnitude due to surface enhanced scattering mechanisms; we find a maximum
signal when a polariton mode lies in the middle of the Stokes shifted emission
band.Comment: 4 pages, 4 figures, submitted PR