Dynamic light scattering at CdSe nanocrystas and CdSe cluster-molecules

High performance dynamic light scattering (DLS) has been used to determine the hydrodynamic diameters of CdSe-nanocrystals as well as CdSe cluster molecules in a size range of 1 to 10 nm. The method enables the determination of the particle sizes including the ligand shells directly in solution. Consistent with the blue shift of the absorption onset by reducing the particle sizes the values for the hydrodynamic radii decrease. For the CdSe nanoparticles the measured sizes were compared with the diameters determined by TEM experiments; the sizes of the cluster molecules were on the other hand estimated from the space filling models of the single crystal X-ray structure determination. Regarding both types of compounds, DLS yield comparable values for the radii, indicating that it provides a potentially important tool in addition to other size determining techniques like TEM, which operates at more drastic conditions, and powder X-ray diffraction being difficult to interpret below 5 nm.