Optical properties of water-soluble Co2+:ZnS semiconductor nanocrystals synthesized by a hydrothermal process

Water-soluble ZnS:Co2+ nanocrystals (NCs) were synthesized by a low temperature hydrothermal process using 3-mercaptopropionic acid (MPA) as capping agent and the influence of doping on the optical properties of ZnS:Co2+ NCs was investigated. It was found that the ZnS:Co2+ NCs are highly crystalline and show zinc blende structure with an average particle size of about 7 nm. The lattice constant of the ZnS:Co2+ NCs decreases slightly by the introduction of Co2+. The Co dopants were well doped into the ZnS:Co2+ NCs, as confirmed by X-ray photoelectron spectroscopy(XPS) and the (4)A(2)(F) -> T-4(1)(P) transition of Co2+ was detected from the UV-vis absorption spectra. The absorption edge of the ZnS:Co2+ NCs is blue-shifted as compared with that of bulk ZnS, indicating the quantum confinement effect. The PL intensity of the NCs shows the maximum value when the Fe-doping concentration is 0.5 at.%. (C) 2011 Elsevier B.V. All rights reserved.