Gap-Plasmon Enhanced Gold Nanoparticle Photoluminescence

Gap-plasmon-enhanced gold nanoparticle photoluminescence is studied experimentally at the single-particle level. The photoluminescence spectra of gold nanoparticles on an Al2O3-coated gold film under both 532 and 633 run excitation show a clear peak near the measured gap-plasmon resonance wavelength. Comparing the collected emission spectrum with that from a gold reference film under 633 nm excitation, a peak photoluminescence enhancement factor of 28 000 is observed. The spectral shape and absolute magnitude of the enhancement factors for both excitation wavelengths are reproduced using numerical calculations without the use of any free parameters. The photoluminescence enhancement is explained in terms of a gap-mode-enhanced e h pair generation rate and a wavelength-dependent enhancement of the emission efficiency.