Cobalt-doped wurtzite ZnS nanocrystals were prepared by a novel and facile synthesis method at temperatures as low as 150 degrees C. The structural and optical properties of prepared CoxZn1-xS (0.0025 <= x <= 0.1) nanocrystals have been characterized. X-ray diffraction patterns and high-resolution TEM images reveal pure hexagonal ZnS phase with size of about 5 nm for all CoxZn1-xS nanocrystals. Room temperature photoluminescence (PL) measurements show that the overall PL intensity is quenched with increasing Cobalt concentration. Deconvoluted PL spectra show three common peaks for pure ZnS nanocrystals, which are originated from Zn or S defect states. An additional peak at 459 nm (blue) observed in CoxZn1-xS nanocrystals is probably arising from the recombination between the shallow donor level and the new dopant level. (C) 2009 Elsevier B.V. All rights reserved.