The quantum yield of a metallic nanostructure of dimer

In this paper, a nanostructure of a metallic dimer is studied, which consists two nearby metallic nanoparticles, to find the possibility for the enhancement of a single molecule's fluorescence by this nanostructure. A simple model, an oscillating dipole within the gap of a metallic dimer, is used to simulate an excited molecule interacting with the dimer in the frequency range of UV to NIR. With the aid of a set of new surface integral equations, the electromagnetic fields in the proximity of the dimer are solved by the boundary-element method (BEM). The quantum yield, the ratio of the radiative power to the total power generated from the dipole, is used to evaluate the efficiency of the dipole's emission. The results of BEM show that the quantum yield of a metallic dimer is better than a single nanoparticle, even though the gap is very small. In addition, a metallic dimer behaves like a low-pass filter which allows most of the dipole's energy of the long-wavelength part radiate to the far field. In contrast, for the short-wavelength part, the nonradiative part is dominant; i.e. most of the dipole's energy is dissipated into Joule's heat inside the metallic dimer in high-frequency range. Two noble metals, Au and Ag, are used for the dimer, and both of them exhibit the same tendencies.