Optical and Thermal Properties of Ib-VI Nanoparticles

Stefanie Dehnen, Andreas Eichhofer, John F. Corrigan, Olaf Ruhr, and Dieter Fenske 

1 Optical Spectra of Selenium-Bridged and Tellurium-Bridged Copper Clusters 

The discrete molecular cluster species presented are ideal subjects for the study of the molecular quantum size effect [1], which is one of the most important questions prompting research in this area of cluster chemistry. It is necessary, therefore to explore the electronic properties of the cluster species, beginning with the interplay of cluster size and HOMO-LUMO gap. A number of theoretical investigations have provided the preliminary answers to this question [2, 3]. The first dipole- and 

The crystals that are obtained from the cluster formation reactions are intensely colored. In fact, the intensity of the color increases when going from sulfur- to selenium- to tellurium-bridged compounds (see below), as might be expected for an increase in the covalent or (semi-) metallic binding properties. Small copper sulfide and selenide clusters form light red, orange, or purple crystals, but with increasing cluster size the color varies from dark red to reddish-black to (finally) black with a metallic sheen. The optical spectra of some copper selenide cluster compounds have been studied by means of solid-state UV-visible spectroscopy. 

A remarkable shift can be observed in the onset of absorption to higher wavelengths, by approximately 0.8 eV, with increasing cluster size (this is related to the increase in the number of copper and selenium cluster core atoms) in this narrow size regime, from approximately 600 nm (2.1 eV) for 1 (39 cluster core atoms) to 

---