Control of fluorescence enhancement and directionality upon excitations in a thin-film system

Nanostructures with various configurations have been extensively used to engineer the emission properties of embedded fluorophores, but lack the flexibility to dynamically control fluorescence. Here we report a thin-film cavity system, comprising a quarter wavelength thick dye-doped dielectric coating on a reflecting surface, in which the fluorescence enhancement and directionality can be significantly modified by altering the illumination angle. The configuration of the cavity yields absorption properties that are highly dependent on illumination angles, due to the coupling between molecular absorption and Fabry-Perot resonances. Therefore the fluorescence intensity relating to the angle-dependent absorbing efficiency varies with illumination angles. In addition, as a result of synergy between intrinsic absorption of the reflecting surface, Fabry-Perot and surface-plasmon-polariton resonances and illumination-angle dependent excitation efficiencies for differently located molecules, the global emission intensity, including emission from dyes at all locations, can be directionally redistributed by altering the illumination angle.