One-pot aqueous-phase synthesis of ultra-small CdSe/CdS/CdZnS core-shell-shell quantum dots with high-luminescent efficiency and good stability

We describe the preparation and structural characterization of ultra-small water-dispersible CdSe semiconductor nanocrystal quantum dots (QDs), which are covered by a double-shell structure from CdS and CdZnS through a one-pot microwave-assisted synthesis technique. Because of the radial increase of the respective valence-and conduction-band offsets, the resulting core-shell-shell CdSe/CdS/CdZnS QDs are well electronically passivated, which endows them with high-fluorescence quantum yield of 90 % and high crystallinity, as was investigated by optical characterization, X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Also, due to the stepwise adjustment of the lattice parameters in the radial direction, the obtained QDs display remarkable photostability, acid stability, and oxidation stability both in the aqueous solutions and the intracellular environment. The cytotoxicity experiment further substantiates the good biocompatibility of the core-shell-shell particles, though the size of the obtained QDs was very small (about 3.2 nm). This implied that the CdSe/CdS/CdZnS core-shell-shell QDs can be used as a promising candidate for fluorescent QDs-based biological applications.