Exciton-Plasmon Interactions and Fano Resonances in Nanostructures – Alexander Govorov

Date: Mon. October 4th, 2010, 12:30 pm-1:30 pm
Location: Rockefeller 221

Coulomb and electromagnetic interactions between excitons and plasmons in nanocrystals cause several interesting effects: energy transfer between nanoparticles (NPs), plasmon enhancement, reduced exciton diffusion in nanowires (NWs), exciton energy shifts, Fano interference effect, and non-linear phenomena [1-3]. Using transport equations for excitons, we model exciton transfer in NWs and explain the origin of the blue shift of exciton emission observed during recent experiments with hybrid NW-NP assemblies [2]. We also look at optical responses of artificial light-harvesting complexes composed of chlorophylls, bacterial reaction centers, and NPs [3]. We show that, using superior optical properties of metal and semiconductor NPs, it is possible to strongly enhance the efficiency of light harvesting in such complexes [3]. An interaction between a discrete state of exciton and a continuum of plasmonic states can give rise to interference effects (Fano-like asymmetric resonances and anti-resonances). These interference effects greatly enhance visibility of relatively weak exciton signals and can be used for spectroscopy of single nanoparticle and molecules. In a nonlinear regime, the Fano effect becomes strongly amplified and results in interesting non-linear responses [4]. If an exciton-plasmon system includes chiral elements (chiral molecules or nanocrystals), the Fano-like interference effects strongly enhance the circular dichroism signals [5,6]. In conclusion, our theory explains current experimental results and also provides rationale for future experiments and applications. Potential applications of dynamic exciton-plasmon systems include sensors and light-harvesting.
1.A. O. Govorov, G. W. Bryant, W. Zhang, T. Skeini, J. Lee, N. A. Kotov, J. M. Slocik, and R. R. Naik, Nano Letters 6, 984 (2006).
2.J. Lee, P. Hernandez, J. Lee, A. Govorov, and N. Kotov, Nature Materials 6, 291 (2007).
3.A. O. Govorov and I. Carmeli, Nano Letters 7, 620 (2007).
4.M. Kroner, A. O. Govorov, S. Remi, B. Biedermann, S. Seidl, A. Badolato, P. M. Petroff, W. Zhang, R.Barbour, B. D. Gerardot, R. J. Warburton, and K. Karrai, Nature 451, 311 (2008).
5.A.O. Govorov, Z. Fan, P. Hernandez, J.M. Slocik, R.R. Naik, Nano Letters 10, 1374 (2010).
6.Z. Fan, A.O. Govorov, Nano Letters, DOI: 10.1021/nl101231b (2010).