Correlating Multiphoton-Absorption-Induced Luminescence (MAIL) with Morphology in Noble-Metal Nanostructures*

The optical properties of nanostructured noble metals differ drastically from those of their bulk counterparts due to surface plasmon (SP) resonance. When incident light couples with the SPs of a noble-metal nanoparticle, it gives rise to strong, localized electromagnetic field enhancement. In particular, surfaces with high curvature experience especially strong field enhancement. Silver and gold SP absorption cross sections lie in the visible region, which make nanostructures of these metals ideal for studying optical phenomena. Multiphoton-absorption-induced luminescence (MAIL) is a nonlinear optical phenomenon that involves ultrafast pulses of light impingent on a nanostructured surface. The SP field enhancement allows for more efficient multiphoton absorption, and highly-efficient, broadband luminescence over the visible spectrum is produced as a result. We examine how the morphologies of noble-metal nanostructures correlate with their MAIL signals. Specifically, we focus on silver nanodendrites, synthesized from galvanic displacement reactions, and gold nanorings and nanotriangles, grown through colloidal synthesis. The absorption order, intensities, and spatial distribution of MAIL signals are examined for different morphologies.