Enhanced luminescence by second-harmonic surface plasmon resonance

Strong ultraviolet luminescence having intensity comparable with device-quality GaN epifilms has been observed in Au nanoparticles. It is identified that the luminescence involves radiative recombination of electrons in band 6 (sp conduction band) with holes in band 4 (secondary top d band), near the L symmetry point. We show that the strong emission is a consequence of the second-harmonic surface plasmon resonance (SHSPR), which is an inherent nature of metallic nanoparticles with high density of surface plasmons. For the SHSPR, we only need a weak pumping source to trigger the second harmonic absorption of very dense surface plasmons in Au nanoclusters. In addition to emissions of Au nanoparticles, SHSPR provides a very efficient way to enhance the luminescence of composites with metal nanoparticles. Incorporation of Au nanoparticles into SiO₂ nanoparticles can enhance the luminescence intensity by two orders of magnitude. SHSPR can serve as one of the underlying mechanisms responsible for surface-enhanced nonlinear optical phenomena.