Appl. Phys. Lett. 102, 133110 (2013)

The emission rate of a light emitter can be enhanced by placing it near a metal surface. However, if an emitter is placed too close to a metal, its emission can be 'quenched' by excited states decaying via nonradiative channels. This occurs because of coupling to high-loss modes in the metal that rapidly convert electromagnetic energy into thermal energy. There is therefore an optimum distance of an emitter from a metal surface at which the emission enhancement is maximized. Esmaeil Heydari and colleagues in Germany have now reduced quenching by fabricating an optimal-thickness spacer layer between a gain medium and gold nanoparticles. The thickness of the spacer layer tunes the coupling between the gain medium and the metal particles, which controls the level of quenching. Their set-up contains 80-nm-diameter gold particles in a colloidal solution on a glass slide. The gold particles were spin coated with polyvinylpyrrolidone to create spacer layers with thicknesses of 15–70 nm. An optically active polymer containing toluene was then spin-coated onto the polyvinylpyrrolidone spacer layer. When optically pumped at 532 nm, the hybrid polymer–gold system lased at a wavelength of 633 nm; optimal performance was obtained for a 30-nm-thick spacer layer.