Loss-Mitigated Collective Resonances in Gain-Assisted Plasmonic Mesocapsules

Inherent optical losses of plasmonic materials represent a crucial issue for optoplasmonics, whereas the realization of hierarchical plasmonic nanostructures implemented with gain functionalities is a promising and valuable solution to the problem. Here we demonstrate that porous silica capsules embedding gold nanoparticles (Au NPs) and fabricated at a scale intermediate between the single plasmonic nanostructure and bulk materials show remarkable form function relations. At this scale, in fact, the plasmon gain interplay is dominated by the location of the gain medium with respect to the spatial distribution of the local field. In particular, the hollow spherical cavities of these structures allow regions of uniform plasmonic field where the energy transfer occurring between chromophoric donors and the surrounding plasmonic acceptors gives rise to a broadband attenuation of losses.