Water-soluble CdSe/CdS and CdSe/Cd _x Zn_1−x S quantum dots with tunable and narrow luminescent spectra and high photoluminescence efficiency

Nearly monodisperse CdSe/CdS and CdSe/Cd _x Zn_1−x S core–shell quantum dots (QDs) were synthesized by the epitaxial growth of CdS or Cd _x Zn_1–x S shells on pre-synthesized CdSe cores through a facile organic route. The thickness effect of CdS and Cd _x Zn_1−x S shells on the properties of resulting core–shell QDs, such as the photoluminescence (PL) efficiency, PL full width at half-maximum (fwhm), and PL decay lifetime, were investigated. The PL efficiency is greatly enhanced from 9 % of CdSe cores to 64 % of CdSe/Cd _x Zn_1−x S core–shell QDs. The PL spectra are narrowed after coating (fwhm ~28–32 nm). The alloy Cd _x Zn_1−x S shell is especially effective to enhance the PL efficiency, and it leads to a smaller red-shift in PL spectra compared with that of the CdS shell. The water-soluble CdSe/Cd _x Zn_1−x S core–shell QDs were obtained by the encapsulation of amphiphilic poly(styrene-co-maleic anhydride) (PSMA)–ethanolamine (EA) polymers, which was initially dispersed in oil phase. It was found that the CdSe/Cd _x Zn_1−x S QDs in water still retained a high PL efficiency as well as a small value in fwhm after encapsulating the CdSe/Cd _x Zn_1−x S QDs with PSMA–EA polymers, expanding the applications of these core–shell QDs in aqueous environment.