Enhanced luminescence by second-harmonic surface plasmon resonance

Strong ultraviolet luminescence having intensity comparable with device-quality GaN epifilms has been observed in An 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.