The Mn(2+)-doped ZnS nanoparticles stabilized by sodium citrate were synthesized through a simple chemical route. Using the ZnS:Mn nanoparticles as seeds, the silica-coated ZnS:Mn nanocomposites were formed in isopropanol by the controlled hydrolysis of tetraethyl orthosilicate. The photoluminescence spectra confirmed that the Mn(2+) ions were incorporated into the ZnS nanoparticles. The annealing effect on the structural and optical properties of these particles was studied over a range of 100-400 degrees C, The results of X-ray diffraction and photoluminescence showed that the silica shell not only improved the thermal stability but also resisted the lattice-deformation and oxidation of the particles. The thermal analysis further confirmed that the non-coated ZnS:Mn nanoparticles were unstable beyond 200 degrees C. 2005 Elsevier Ltd. All rights reserved.