Controlled optical properties of water-soluble CdTe/CdS/ZnS quantum dots

Core–shell–shell quantum dots (QDs) of CdTe/CdS/ZnS having an average diameter of 4.2 nm and exhibiting type-II behaviors have been facilely synthesized in water via a one-pot technique. Water-dispersible CdTe/CdS/ZnS QDs have been prepared simply by injecting Zn2+(aq) into an aqueous colloidal solution of CdTe/CdS core–shell QDs having an average diameter of 3.8 nm, which were already synthesized and stabilized in water with assistance of 3-mercaptopropionic acid. The optical properties of CdTe/CdS/ZnS QDs have been controlled by adjusting reaction time as well as pH, reaction temperature, and Zn2+ amount. The band-gap energy of CdTe/CdS/ZnS core–shell–shell QDs decreases gradually from 2.25 to 2.07 eV as the reaction time changes from 0 to 720 min. The photoluminescence spectrum of CdTe/CdS/ZnS core–shell–shell QDs shifts to the red steadily from 538 to 613 nm as the reaction time changes from 0 to 720 min. Photoluminescence has been found to be the most efficient when CdTe/CdS/ZnS core–shell–shell QDs were grown for 6 h at pH 10.6 and 100 °C with [Zn]/[Cd] of 1/300. The photoluminescence quantum yield of the aqueous colloidal solution of CdTe/CdS/ZnS core–shell–shell QDs has been found to be as large as 15 %, whereas that of CdTe/CdS core–shell QDs has been observed as 4 %.