Ultrasonic-assisted synthesis of aqueous CdTe/CdS QDs in salt water bath heating

• Ultrasonic promotes formation of crystal nucleus and QDs were synthesized in 0.5 h.
• The new heating method provides a PLQY of up to 97.13%.
• The synthesis mechanism of the core shell structure of the CdTe/CdS QDs was inferred.
• The preparation method was efficient, simple and clean.

A novel simple method for fast and efficient synthesis of aqueous CdTe/CdS quantum dots (QDs) with core–shell structure was developed by using salt water bath heating with the ultrasonic-assisted technique in this paper. The formation of crystal nucleus was promoted by ultrasonic and CdTe/CdS QDs with blue fluorescence were synthesized only in 0.5 h. The heat source was bath heating in salt water solution at 60% NaCl and the heating temperature could reach 105 °C. The heating method solved the biggest drawback of low photoluminescence quantum yield (PLQY) of ordinal bath heating in water. The preparation was cheap, simple and had less pollution to the environment. The properties of the CdTe/CdS QDs were thoroughly investigated by ultraviolet–visible (UV–vis), photoluminescence (PL), transmission electron microscope (TEM), laser size analysis, fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Different CdTe/CdS QDs with core shell structure were efficiently synthesized and the maximum PLQY could reach 97.13% when refluxing at 105 °C for 2 h. These QDs exhibited uniform dispersity, high fluorescence intensity, good optical property and long life of fluorescent. The synthesis mechanism of the core shell structure of the QDs was inferred that the Cd2+ might coordinate with sulfur (S) as well as thiol propionate (–SCH2CH2COO−1) to constitute two relatively thick compound layers on the QDs surface as passive shells.