Light emission from single gold nanorods excited by continuous wave lasers was investigated by using ultra-narrow-band notch filters to obtain their complete spectral shape. The spectral profile of Stokes emission can be fitted by a Lorentzian line shape and that is dominated by localized surface plasmon resonance. Moreover, a clear anti-Stokes emission band can be always observed under different excitation wavelengths. The spectral shape of anti-Stokes emission can be fitted well with a Fermi-Dirac like line shape. Electron Fermi-Dirac distribution should influence the spectral shape of anti-Stokes emission for both interband and intraband transitions. It was also found that the intensity of anti-Stokes emission increases more rapidly in comparison with that of Stokes emission as illumination power increases on resonant excitation. This phenomenon can be understood as the temperature dependent of the electron Fermi-Dirac distribution due to photothermal effect.
Luminescence quantum yields (QYs) of gold nanoparticles including nanorods, nanobipyramids and nanospheres are
measured elaborately at single nanoparticle level with different excitation wavelengths. It is found that the QYs of the
nanostructures are essentially dependent on the excitation wavelength. The QY is higher when the excitation wavelength
is blue-detuned and close to the nanoparticles’ surface plasmon resonant peak. A phenomenological model based on
plasmonic resonator concept is proposed to understand the experimental findings. The excitation wavelength dependent
of QY is attributed to the wavelength dependent coupling efficiency between the free electrons oscillation and the
intrinsic plasmon resonant radiative mode. These studies should contribute to the understanding of one-photon
luminescence from metallic nanostructures and plasmonic surface enhanced spectroscopy.
Strong Stokes and anti-Stokes one-photon luminescence from single gold nanorods is measured in experiments. It is found that the intensity and polarization of the Stokes and anti-Stokes emissions are in strong correlation. Our experimental observation discovered a coherent process in light emission from single gold nanorods. We present a theoretical mode, based on the concept of cavity resonance, for consistently understanding both Stokes and anti-Stokes photoluminescence. Our theory is in good agreement of all our measurements.