Additional peak appearing in the one-photon luminescence of single gold nanorods

We used a confocal laser microscope to investigate the one-photon photoluminescence (PL) of gold antennas. The PL spectra can be precisely fitted to a plasmon-enhanced PL model. For increasing the antenna length, the energy peak position decreases continuously until it reaches a value of 1.7-1.8 eV. For longer antennas and smaller plasmon energies, we observe an additional, persistent shoulder in the PL spectra, which we explain by a Gaussian-shaped peak at Δ_X≈1.78-1.79  eV. We attribute this behavior to the opening of an additional decay path for electrons at the gold interband transition edge, which we observe only for long antennas.