Stable and water-soluble ZnCdS:Mn/ZnS core/shell quantum dots (QDs) with quantum yields over 20% have been synthesized via a one-spot aqueous route. Compared with the ZnCdS:Mn cores, the ZnCdS: Mn/ZnS core/shell QDs exhibited approximately 21.0 times stronger photoluminescence due to the greatly decreased nonradiative decay rate. A corresponding synthetic mechanism for such enhancement is discussed in detail. Furthermore, the bandgap energy of the ZnCdS: Mn/ZnS QDs is tuned to a lower level by increasing the Cd concentration in the cores, and the applicability for preparing QD-LEDs with high lumen efficiency is also described. (C) 2010 Elsevier B.V. All rights reserved.