Enhanced spontaneous light emission by multiple surface plasmon coupling.

Photoluminescence of polyfluoren copolymers, a white-light material, was demonstrated to be enhanced selectively by coupling with either localized or propagating modes of surface plasmon resonance (SPR). The silver sub-micron cylinders with 75nm height fabricated by e-beam lithography followed by e-beam evaporation and lift-off process. The enhanced light emissions at 500nm and 533nm are attributed to the low frequency branch of localized SPR. Furthermore, a 50nm silver thin film between these cylinders and the substrate provides propagating surface plasmons under excitation and enhances the blue emission band of the polyfluoren copolymer at 438nm. This delocalized SPR is sufficient for effective plasmon to light conversion. Moreover, by effectively coupling the localized and propagating SPR, we can experimentally demonstrate that the photoluminescence of polyfluoren copolymers is enhanced by 4 to 5.4 times at different wavelengths compared to enhancement by either single mode.