Light Emission in Plasmonic Nanostructures
Master of Science
Recently, photoinduced light emission from plasmonic nanoparticles has attracted considerable interest within the scientific community because of its potential applications in novel sensing, imaging and most recently in nanothermometry. The light emission from plasmonic nanoparticles has been assigned to the radiative recombination of hot carriers through inter- and intra-band transitions enhanced by surface plasmons. To precisely study the effects of the size on the light emission of nanoparticles, we conducted a systematic size dependent study of gold nanorods with similar aspect ratios and varying widths. Using our single particle photoluminescence and scattering spectroscopy along with correlated SEM images and FDTD simulations, we calculated the quantum yield and Purcell enhancement factors of individual gold nanorods. Our results register a strong size dependence of quantum yield in gold nanorods suggesting higher emission efficiency in smaller gold nanorods compared to that of large ones. Furthermore, our calculations allowed us to separate the contribution of inter- and intra-band transitions into the emission spectra of individual gold nanorods. We observed an increase in the contributions of the geometry-assisted intraband transitions in the emission of 20-30 nm wide gold nanorods. Our FDTD simulations of the electric field distribution of gold nanorods in the near field also demonstrates that electric field confinement is 2.3 times stronger in smaller gold nanorods. Such confinement can provide the necessary momentum mismatch to excite electrons efficiently through intraband transitions. This prediction agrees well with our experimental observations.
photoluminescence; gold nanorod; plasmonics; Purcell factor