Enhancement of Emissive Processes and Nonlinearities

Abstract

corded [Kneipp et al., 1997, Nie and Emery, 1997], with estimated enhance- ments of the scattering cross section by factors up to 1014. The majority of this enhancement is believed to arise from the highly enhanced fields in metal nanoparticle junctions due to localized surface plasmon resonances. Termed hot spots, these highly confined fields also enable an increase of fluorescent emission, albeit with more modest enhancement factors. A proper understand- ing and control over the generation of these hot spots, for example in the form of nanoscale plasmonic cavities, is currently one of the major driving forces behind the design of nanoparticle ensembles with tuned optical properties. This chapter will focus mainly on the fundamentals and geometries for SERS due to localized plasmon modes in metal nanostructures. Theoretical modeling based on scattering-type calculations will be reviewed, and addition- ally a cavity model for SERS presented, which aims to provide a general de- sign principle and scaling law for this light-matter interaction. The related en- hancement of fluorescence from emitters placed into the near-field of metallic nanostructures, as well as quenching processes due to non-radiative transitions, are treated as well. Enhancement of the intrinsic luminescence of noble metal nanoparticles and nonlinear processes are discussed at the end of this chapter.