Limits of luminescence efficiency enhancement by surface plasmon polaritons

We develop a rigorous theory of the enhancement of spontaneous emission from a light-emitting device via coupling the radiant energy in and out of surface plasmon polaritons (SPPs) on the metal-dielectric interface. We show that while the efficiency of coupling into the SPP mode can be quite high, the radiative efficiency of the SPP itself is relatively low, with a substantial fraction of the energy lost in the metal. Using the GaN/Ag system as an example we obtain easy-to-interpret analytical results that unequivocally indicate that using SPP pays off only for emitters that have medium-to-low luminescence efficiency; thus the SPP applications should be limited to those in sensing and analysis rather than in the development of efficient light sources.