Optical Emission and Energy Transfer in Nanoparticle-Nanorod Assemblies: Potential Energy Pump System for Negative Refractive Index Materials

Gold nanorods (NRs) in different arrangements represent the most plausible system for the creation of negative refractive index materials (NIMs) in the optical frequency range. Among other challenges, one of the major limitations of present day NIMs is their large amount of energy dissipation which frustrates the restoration of near field modes. To take advantage of exciton-plasmon interactions, an optical system consisting of semiconductor nanoparticles (NPs) and Au NRs can continuously pump energy into the NIM resonator. Superstructures with promising properties were achieved by assembly of CdTe nanoparticles on the surface of nanorods by using streptavidin-biotin bioconjugation where NP -> NR energy transfer occurs with great efficiency. On the initial layer of bioconjugated NPs, the second layer is formed due to nonspecific interactions, which is manifesting in unusual spectral behavior and dependence of lifetime on NP concentration. By varying the ratio of NPs per NR, the amount of energy transfer can be controlled, while the diameter of NPs and wide overlap offers the possibility to tune the wavelength of the pumping light.