Directional Fluorescence Emission Mediated by Chemically-Prepared Plasmonic Nanowire Junctions

The localized interaction between metallic nanostructures and surrounding fluorescent molecules can influence the emission characteristics of the molecule. With this hindsight, herein, by employing a Fourier optical fluorescence microscope, we experimentally show how fluorescence emission from molecules in the vicinity of a chemically prepared silver nanowire-dimer-junction can be directed in one or two channels. Measured forward-to-backward ratio of the fluorescence emission in a single channel was as high as 4.3 dB, and the observed polar and azimuthal angular spread was as narrow as 15° and 60°, respectively. Interestingly, the angle between the two emission channels mimicked the angle between the nanowires, thus, highlighting the prospect of geometrical control of the emitted light. These observations were further corroborated by three-dimensional finite-difference time-domain simulations. The presented results will have implications in momentum-space engineering of molecular fluorescence emission and can be extrapolated to single-emitter studies.