ZnS nanoparticles of diameters of 3-4 nm were self-assembled to form dense nanospheres of sizes similar to 100 nm by a colloidal precipitation method using PVP as the stabilizing agent. Studies indicated that the ZnS nanoparticles maintained their individual properties inside the nanospheres. Optical absorption spectra of the samples demonstrated the effect of quantum confinement in the ZnS nanocrystals. Room temperature photoluminescence measurements showed a sharp UV emission at similar to 370 nm, attributed to sulfur vacancies. (C) 2007 Elsevier B.V. All rights reserved.