Colloidal ZnSe, ZnSe/ZnS, and ZnSe/ZnSeS Quantum Dots Synthesized from ZnO

Colloidal ZnSe quantum dots were successfully synthesized from ZnO in a lauric acid/hexadecylamine mixture. X-ray diffraction patterns indicated that the ZnSe quantum dots possess a wurtzite structure. Transmission electron microscope images of the quantum dots showed that the average diameter are in the range of 25∼60 A. The size-dependent photoluminescence was controlled from 400 to 440 nm with the quantum yields of 6∼10% at room temperature. After passivation with 1.8 monolayer of ZnS overcoat by a traditional two-step method, the quantum yields of ZnSe/ZnS QDs are increased ∼4.5-fold (quantum yield ∼32%). An in-situ method of overcoating was done by directly injecting TOPS into the flask containing ZnSe, ZnO/lauric acid/hexadecylamine, and TOPSe. The photoluminescence quantum yields were improved ∼3.8-fold after introduction of 1.6 monolayer ZnSeS overcoat to the ZnSe QDs.