Water-soluble CdSe/CdS and CdSe/Cd _x Zn_(1-x) S quantum dots with tunable and narrow luminescent spectra and high photoluminescence efficiency

摘要

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.