Radiative Decay Rate Enhancement and Quenching for Multiple Emitters near a Metal Nanoparticle Surface

When molecules (emitters) are placed near a metal surface, their Raman scattering will be significantly enhanced, and their fluorescence signal might be enhanced or quenched. Both these two phenomena are closely related to the enhancement of the radiative decay rate (RDR) of the molecules upon the presence of a nearby metal nanoparticle. Using a recently developed model, we found that the RDR enhancement or quenching for two or more emitters placed near a spherical Ag nanoparticle surface is drastically different from that when only one emitter is included. When three emitters are arranged near the metal surface, the overall enhancement factor can be even much smaller than the lowest enhancement factor of one emitter. If six emitters are evenly arranged near the metal surface, the enhancement factors at different wavelengths exhibit an asymmetric line shape near the resonance wavelength of the metal nanoparticle and the line shape will converge when the number of emitters is increased further. When emitters are placed at different distances from the nanoparticle surface, the coupling between one emitter and the metal nanoparticle along the dipole axis exhibits a near-field characteristic, while the enhancement factor of the RDR for six emitters arranged evenly around a metal nanoparticle follows a far-field trend. The discoveries will advance our fundamental understanding of the enhancement and quenching mechanism of emitters near metal nanoparticle surfaces, especially for those with a high quantum yield which allows more than one of them to radiate simultaneously near one metal nanoparticle surface.