Dual-Band Plasmonic Enhancement of Ag-NS@SiO₂ on Gain Medium's Spontaneous Emission

We present a theoretical study on plasmonic enhancement of molecular fluorescence near a nanocomposite, Ag nanoshell (Ag-NS) coated by a gain medium of molecule-doped SiO₂ layer. We use an average enhancement factor (AEF), which considers contributions from all possible orientations and locations of molecules in the silica layer to estimate the overall performance of Ag-NS@SiO₂ at specific excitation and emission wavelengths. Our results on the AEF reveal that Ag-NS@SiO₂ is a dual-band enhancer on the spontaneous emission of the gain medium; one is a narrowband in a shorter wavelength regime (quadrupole mode) and the other is a broadband in a longer wavelength regime (dipole mode). These two bands are tunable by adjusting the core size and the thickness of the Ag shell. Due to this merit, Ag-NS@SiO₂ has great potentials to enhance Forster resonance energy transfer between a donor and a corresponding acceptor with large Stokes shifts.