Dipolar emitters at nanoscale proximity of metal surfaces: Giant enhancement of relaxation in microscopic theory

Recently, there has been explosive growth of nanoscience and nanotechnology. Nanosystems possess unique properties different from those of macroscopic materials when characteristic lengths governing their properties ~e.g., electron mean-free path l tr , the exciton Bohr radius, Debye radius r D , etc.! become comparable to geometric sizes of the particles or distances between them. Then macroscopic description of nanostructured system may not be applicable even on the order of magnitude. In this Rapid Communication, we consider a dipole emitter @semiconductor quantum dot ~QD!, dye molecule, atom, or rare-earth ion# at a nanometer-scale distance from the surface of a metal. We treat the metal microscopically in local random-phase approximation ~LRPA!. We found giant enhancement of the nonradiative decay of excitations in such emitters due to Coulomb interaction with electrons in the metal. In a nanometer-scale proximity to metal, this enhancement is an order of magnitude greater than in the existing theory, 1‐3 that treats the metal as dielectric medium. We call such an approach, where the dielectric function possesses temporal but not spatial dispersion, as dielectric medium approximation ~DMA!. Unique properties of QD’s make them attractive candidates for various optical applications from optical amplification and lasing 4,5 to fluorescence tagging. 6 While some ap