Plasmonic mode interactions with organic semiconductor gain media in nano-confined geometries

Abstract

Coupling of gain materials to metallic nanostructures and thin films offers an avenue for amplification of plasmonic modes in both confined and extended geometries. In the past decade, a deeply sub-wavelength analogue to the laser, using surface plasmons instead of photons, has been proposed and demonstrated. Additionally, propagating surface plasmon polaritons on extended metallic films have been amplified using gain media to achieve chip-scale propagation lengths. Here, we investigate a core-shell nanoparticle structure amenable to amplification of resonant surface plasmon modes using a gold nanorod as the core and an organic polymer semiconductor gain medium as the shell. Organic semiconducting polymer gain media are of interest because, unlike laser dye molecules, they do not undergo significant concentration quenching in the solid-state and, therefore, can result in a high chromophore density in the optical near-field of the metal nanostructure. For investigations of resonant surface plasmon mode amplification, we fabricate gold nanorod-F8BT core-shell nanoparticles through a miniemulsion synthesis process. A more distinct threshold in emitted intensity as a function of optical pump energy is observed from these hybrid structures and neat F8BT nanoparticles compared to dissolved F8BT molecules. However, spectral narrowing is not observed from these structures, potentially due to the low heterostructure yield and poor spectral overlap between the absorption and emission bands of the F8BT with the pump laser and the longitudinal surface plasmon resonance of the nanorods, respectively. Future work will focus on increasing heterostructure yield, employing a red-emitting gain material such as MEH-PPV to couple to longitudinal surface plasmon modes and alternative thin-film geometries in which plasmonic mode-emitter interactions can be easier to control.