Plasmonic enhancement of coreshell (Au@SiO_2) on molecular fluorescence

摘要

The overall performance of a large number of coreshells (Au@SiO_2) on the fluorescence of molecules doped within the silica shell is studied theoretically by considering the random orientation and location of the molecules to calculate the average enhancement factor (AEF). Using Mie's theory, the component of the intensified electric field along the dipole's orientation at the molecular location in the presence of the coreshell, irradiated with polarized light, is calculated for analyzing the molecular excitation rate. In addition, using dyadic Green's functions, the analytical solution of the electromagnetic field induced by an arbitrarily oriented and located electric dipole embedded in the shell is derived to simulate the radiative and non-radiative decay rates of an excited molecule, and then the apparent quantum yield of the system is obtained. Combining the two solutions, the enhancement factor (EF) is evaluated. Furthermore, AEF is calculated by averaging the individual EF over all possible orientations and positions of the molecules. Our results indicate that the AEF of Au@SiO_2 is much lesser than the maximum EF, and it behaves as a low-frequency enhancer with a cutoff wavelength of 590nm.