Fluorescent silver oligomeric clusters and colloidal particles

Highly luminescent single colloidal silver nanoparticles under blue excitation were detected. The intense luminescence observed from the single particles is attributed to different emissive centers. Picosecond lifetimes of those single nano-objects have been measured. Comparison with colloidal particles emission formed in aqueous solution, using polyacrylate polyanion as stabilizer is drawn. The optical properties of silver colloidal particles in solution are observed while their surface is changed by deposition of silver ion. A large visible emission under UV or surface plasmon region excitations is observed for Agn@Ag+, while no fluorescence emission was found for Agn or Ag+ systems. The intense visible light emission changes should primarily come from chemical surface active sites. It was observed that the oligomeric clusters, composed of only few atoms Ag4+xx+ and Ag73+, have a substantial emission in the same visible region. A model which ascribes the photoemission of the chemically modified silver colloidal particle to oligomeric clusters on the Ag particle surface is proposed. Those emissive water soluble silver clusters have potential for biological labelling, and light emitting sources in nanoscale optoelectronics applications.