The optical properties of small metal clusters consisting of tens of atoms often differ from those of the same materials in bulk form. The clusters behave more like molecules than metals, with discrete transitions between electronic states that are associated with characteristic emissions. Gold nanoclusters that are fluorescent have been prepared, but the distribution of particle sizes was too broad and the emission efficiency too low for practical application.
Zheng et al. describe the synthesis of monodisperse eight-atom gold clusters that emit blue light with 100 times higher efficiency and that may be usable as fluorophors. The Au8 clusters are encapsulated in dendrimers (macromolecules with a treelike branched structure), forming stable nanodots, which are smaller than nanoparticles. In samples containing a range of cluster sizes, fluorescence was directly proportional to the relative abundance of Au8, indicating that this octet alone is responsible for the blue emission.—JFU
J. Am. Chem. Soc. 10.1021/ja035473v (2003).