The Enhancement of Spontaneous Emission by the Surface Plasmon Resonance of Metallic Nanostructures (II)

The research is a two-year project, from Aug. 2008 to July 2010, which is the extension of the previous project (NSC 96-2221-E-182-021). The main goal is to study the enhancement or quenching of molecular fluorescence (or quantum dot’s photoluminescence) by the surface plasmon resonance of a nearby metallic nanostructure, when they are irradiated by an illuminating light. Numerical Simulation A set of new surface integral equations is derived to study the optical responses of the near-field and far-field of multi-metallic nanoscatterers for 3D problems. In particular, these nanostructure with coupled surface plasmon resonance are concerned, e.g. a dimer, linear nanoantenna, bowtie nanoantenna and symmetric nanolens. Due to the gap mode of these structures, their local field factor and the apparent quantum yield are higher than that of a monomer structure. If a molecule is placed within the gap, these structures can provide a significantly strong electric field to excite it, when they are irradiated by an illuminating light. Once the molecule is excited, the fluorescence is emitted to far field efficiently, because of the high apparent quantum yields of these structures. Therefore we will study their local field factor and apparent quantum yield in details. In addition, the structures of coreshells and coreshelled dimers will also be analyzed. Experiment Using one-photon or two-photon laser excitation, the interactions of Au and Ag nanostructures with dye molecule are investigated to identify the enhancement or quenching for the fluorescence. In order to study the relation of the molecular excitation spectrum to the local field factor and the emission spectrum to the quantum yield of metallic nanostructure, different dye-molecules are used to combine with Au and Ag nanostructures and are irradiated by an illuminating laser of different frequency. A core-shelled nanoparticle will be synthesized by coating a silica-layer on an Au or Ag nanoparticle, and then it will be coated by another outer shell (SiO2) containing several dye-molecules. Using this technique, the distance between the dye-molecules with the metal can be controlled and fixed. This nanostructure will be also studied by the irradiation of laser to study the effect of SPR on the enhancement or quenching of fluorescence. In addition, Au-nanorods with different aspect ratio, which have different surface plasmon resonance frequency, will be synthesized by electrochemical method. These nanorods coated with silica layer will be used to combine with different dye-molecule as a sample, which is studied by using laser-scanning confocal microscopy. Moreover, the lifetime of the fluorescence of the dyes in these coreshelled nanoparticles will be measured to compare with the numerical results.

Project ID:PB9801-2179
External Project ID:NSC97-2221-E182-012-MY2