A room-temperature method for coating a ZnS shell on semiconductor quantum dots

A green room-temperature method based on phase transfer and a reaction between Zn2+ and S2- in toluene for coating a ZnS shell on CdSe and Ag2S quantumdots (QDs), respectively, has been developed. In this method, the S2- anions in Na2S aqueous solution were transferred to toluene via electrostatic interactions between the anions and didodecyldimethylammonium bromide (DDAB), which served as an excellent sulfur precursor and thereby reacted with Zn2+ to form a ZnS shell on the surface of semiconductor QDs in the presence of QDs in an organic phase. After the ZnS shell was coated on QDs, the photoluminescence (PL) intensities of the CdSe and Ag2S QDs were found to increase approximately 12 times and 14 times, respectively, while both the emission wavelengths and the peak shapes were well maintained. The proposed method is novel, simple and robust, providing a green solution to the preparation of ZnS shell-coated QDs.