Cubic CdSe nanoparticles have been prepared using cadmium acetate dihydrate (C4H6CdO4 center dot 2H(2)O) as a Cd2+ ion source and sodium selenosulfate (Na2SeSO3) as a Se2- ion source with the aid of ultrasound irradiation in normal laboratory conditions at room temperature (27 degrees C). Scanning electron microscope (SEM) images display that the product consists of nanocrystallites of about 20 nm which aggregated in the form of polydispersive nanoclusters with dimensions in the range of 150-200 nm. X-ray diffraction analysis exhibits that the particles are excellently crystallized. Energy dispersive X-ray spectroscopy (EDX) measurements further confirms the formation of purely CdSe nanoparticles and average atomic percentage of Cd to Se is about 52:48; showing that the product is almost stoichiometric. UV-visible absorption spectroscopy of the as prepared nanoparticles shows the presence of direct transition with energy band gap of about 2.02 eV. Comparing to 1.74 eV, corresponding to its bulk value, a blue shift of about 0.28 eV is detected which is understood as a quantum size effect, due to confinement of electron and hole in a small volume. (c) 2007 Elsevier B.V. All rights reserved.