Diffraction-limited photogeneration and characterization of silver nanoparticles

Visible-light-induced photogeneration of silver nanoparticles in a diffraction-limited focal region is demonstrated. The photochemical growth depends quadratically on illumination intensity indicative of a multiphoton generation process, with the identity of the silver nanoparticles confirmed by UV/vis absorption spectroscopy. Mie simulations of the absorption spectrum reveal a size distribution dominated by Ag particles with radii in the range of a few nanometers. Spectrally resolved laser excitation and emission studies demonstrate that the likely luminescence source is surface-enhanced Raman scattering from silver nanoparticles, with spectral jumps occurring on a time scale comparable to that of fluctuations in the total luminescence intensity. Possible routes for the photogeneration process as well as identity of the Raman-active species are discussed. Such diffraction-limited photoproduction methods for luminescent silver nanoparticles offer novel routes toward optical data storage and nanometer-scale molecular sensing.