Radiation of a molecular dipole near metal surface is inhibited due to energy transfer from excited molecular orbitals to optically inactive electronic excitations in metal. While for metal films this phenomenon has been extensively studied during past 30 years [1], experiments on single-molecule fluorescence near metal nanoparticles have been performed only recently [2,3] revealing a significant fluorescence quenching even for small nanometer-sized particles. The fluorescence efficiency is determined by a competition between local field enhancement due to localized surface plasmon in a nanoparticle and energy dissipation due to excitation of electron-hole pairs in nanoparticle surface layer.
We performed first TDLDA calculations of radiative and nonradiative decay rates of a molecule in a close proximity to nanometer-sized gold nanoparticle that incorporate all relevant quantum-size effects including Landau damping, surface screening, and electron spillover. The quantum-mechanical non-radiative rate is found to be much higher as compared to semiclassical calculations [4], while radiative rates do not substantially differ, i.e., semiclassical approach significantly overestimates the fluorescence efficiency. At the same time, for small nanoparticles, the nonradiative rate is strongly reduced as compared to that for flat metal surface, resulting in the effective increase of fluorescence efficiency with decreasing nanoparticle size.
[1] R. R. Chance, A. Prock, and R. Silbey, Adv. Chem. Phys. 37, 1 (1978)
[2] E. Dulkeith, M. Ringler, T. A: Klar, J. Feldmann, A. Munoz Javier, W. J. Parak, Nano Lett. 5, 585 (2005)
[3] P. Angel, P. Bharadwaj, L. Novotny, Phys. Rev. Lett. 96, 113002 (2006).
[4] J. Gersten and A. Nitzan, J. Chem. Phys. 75, 1139 (1981).
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