Emission enhancement within gold spherical nanocavity arrays

Abstract

Gold nanocavity arrays were prepared on fluorine-doped tin oxide on glass by electrochemical deposition of gold through monolayers of polystyrene spheres. The impact of the resulting spherical cap architecture on the photophysics of solutions and self-assembled monolayers of luminophore encapsulated within the nanocavities is reported for the first time. From conventional confocal fluorescence microscopy, the emission intensity of solutions of [Ru(bpy)(2)(Qbpy)](2+) (where bpy is 2,2'-bipyridyl and Qbpy is 2,2':4,4'':4,4''-quarterpyridyl) and fullerene (C(60)) encapsulated within the 820 nm diameter nanocavities was demonstrated to increase by approximately an order of magnitude compared with that of the associated bulk solution. Comparison was also made with the emission observed for luminophore solution encapsulated in cobalt nanocavities of comparable dimensions, where plasmonic interactions are not anticipated. Again, approximately an order of magnitude enhancement was observed for the gold arrays. Luminescence lifetime imaging revealed that the enhancement of the emission intensity of this solution within the nanocavity was accompanied by a small but significant decrease in the luminescent lifetime for [Ru(bpy)(2)(Qbpy)](2+). Enhancement was, in addition, strongly influenced by the wavelength of excitation, suggesting that plasmonics may play a role in the enhancement of the excitation process. An important observation from confocal imaging studies was that the dimensions of the luminophore emission field from solution within the cavities were significantly smaller than the dimensions of the cavity aperture and corresponded to a little more than that of the point spread function of the microscope. This indicates that its origin is significantly smaller than the wavelength of the emitted light and suggests that luminescence enhancement is highly localised. When the array was filled with a solution of [Ru(bpy)(2)(Qbpy)](2+) the emission spectrum of this complex was red shifted and broadened compared with that of the bulk solution, typical of the formation of a luminescent surface film. In addition, significant enhancement was only observed when the solution was sonicated into the array. Both these observations suggest that the emission enhancement is localised near the bottom of the cavity. Self-assembled monolayers of [Ru(bpy)(2)(Qbpy)](2+) were formed on the array and approximately 7 orders of magnitude enhancement of the Raman signal was achieved. Significantly, the emission intensity was approximately 4-fold higher for the monolayer than for a solid film under the same conditions, but surface quenching is thought to play a significant role in the observed decrease in lifetime for the monolayer of this complex on the array.

Surface enhanced luminescence and Raman scattering from ferroelectrically defined Ag nanopatterned arrays

“…For Rubpy, low SEL is expected since only a small overlap exists between luminescence absorption and emission with the plasmonic absorption band of the substrate. 31 In contrary, a great enhancement is expected for Rh6G since a significant overlap exists between the luminescence absorption, emission and plasmonic absorption. 32,33 The Raman scattering and luminescence spectra recorded for probe molecules on the Ag nanopatterned array show surface enhancement of luminescence and Raman scattering.…”

Site selective surface enhanced Raman on nanostructured cavities

“…6,9 Metallic sphere segment void substrates sustain surface plasmons, they generate intense electric fields under illumination and consequently show huge enhancements of SERS in air and in contact with solution. 7,10 To date, while studies have been performed in regard to the Raman properties of these substrates, few studies have been performed on luminescence enhancements by these substrates. Furthermore, whereas the angle dependence of surface enhanced Raman signal from such substrates have been widely studied by Bartelett, Cole and Baumberg et al We present the the angle dependence of both SERRS and luminescent signal which were collected simultaneously.…”

“…As reported previously, 10 the depth of the wells has been measured by cutting the sample and imaging the substrate side-on using a SEM. The measured depth of the cavity was determined in this way to be 600 nm.…”

“…7 Gold nanocavity arrays on FTO substrate were prepared using a nanosphere lithographic technique based on electrodeposition through the voids of self-assembled polystyrene spheres on FTO as described previously. 10 The resulting gold nanocavities were investigated using SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) measurements.…”

The Effect of Ag Nanoparticles on Surface-Enhanced Luminescence from Au Nanovoid Arrays

“…The resulting structures have nanovoid architecture such as those reported here. These nanovoid structured surfaces possess spherical cap architecture and are arranged uniformly in a hexagonally close-packed array [16][17][18][19][20][21][22][23][24][25].…”