Enhancement of optical emission and absorption by metal nanoparticles

Abstract

We provide a simple analytical model for the modification of optical properties of active molecules and other objects when they are placed in the vicinity of metal nanoparticles of sub-wavelength dimensions. Specifically, we study the enhancement of optical absorption and emission by these objects. The theory takes into account the radiative decay of the surface plasmon mode supported by the metal nanospheres - a basic phenomenon that has been ignored in electro-static treatment. In addition, the theory adequately treats the quenching effect of high order surface plasmon modes on luminescence efficiency. Using the examples of Ag and Au nanospheres embedded in GaN dielectric, we show that enhancement for each case depends strongly on the nanoparticle size and molecule-nanoparticle separation, enabling optimization for each combination of absorption cross section and original radiative efficiency. The enhancement effect is most significant for relatively weak and diluted absorbers and rather inefficient emitters that are placed at some optimal distances from the metal nanoparticles.