Effective excitation and control of guided surface plasmon polaritons in a conjugated polymer-silver nanowire composite system

This study demonstrates a novel light-emitting conjugated polymer (PCFOz) used to initiate excitation and propagation of surface plasmon polaritons (SPPs) in silver nanowires. Excitons in the polymer optically excited in close proximity to silver nanowires directly couple to the guided SPPs, and then propagate towards the wires' ends and light up. A tunable exciton-plasmon coupling is realized by varying the distance between PCFOz and Ag nanowires. Strongly efficient excitation of SPPs appears in the case of a spacer thickness of similar to 10 nm. Moreover, photobleaching of the organic system is dramatically suppressed by separating the emitter and metal with a spacer, allowing at least 20 times improvement of photostability with a spacer thickness of 25 nm. Spectral dependence of exciton-plasmon coupling indicates that the nanowires' tips contain larger amount of red components. Study of emission decay dynamics demonstrates that the emission properties of PCFOz have been significantly modified by the proximity of Ag nanowires, generating more than 9-fold enhancement of PCFOz spontaneous emission. These results are believed to be important for the development of thin-film photonic-plasmonic waveguides, single photon source and various nanoscale fluorescence sensors.