PbS and ZnS- and Pb(OH)(2)-capped PbS nanoparticles produced in inverted micelles luminesce extremely weakly. Removal of water present during synthesis results in a significant increase in the luminescence quantum yield of the nanoparticles. Water addition to the dried nanoparticles induces efficient luminescence quenching for both uncapped and capped particles. H2O and D2O quench the luminescence of the dried particles with similar efficiencies. We propose a quenching model where water penetrates into the nanoparticle crystal lattice. (C) 2004 Elsevier B.V. All rights reserved.