Surface Plasmon Enhanced Fluorescence of Dye Molecules on Metal Grating Films

Fluorescence enhancement of Rhodamine 6G (R 6G) molecules with a maximal enhancement factor of more than 30-fold was observed on Ag grating films. The enhancement mechanisms arise from both the surface plasmon polariton (SPP) enhanced absorption and surface plasmon coupled emission (SPCE). Time-resolved transient absorption spectroscopy was carried out to first experimentally confirm the SPP-enhanced absorption spectra of R 6G and its angle dependence on metal gratings, which cannot be directly obtained from conventional steady-state measurements. Combined with photoluminescence measurements, we observed how the contributions from two enhancement mechanisms to fluorescence emission varied with excitation incident angle and grating period. For larger grating period, the SPP-enhanced absorption becomes weaker and SPCE turns to the dominant mechanism for fluorescence enhancement. The wavelength resolution ability of SPCE makes it useful for potential applications such as wavelength-ratiometric measurements and fluorescence sensing.