Luminescent Cd1−xZnxS quantum dots synthesized by a nanoemulsion method, assisted by an ultrasonic probe

A series of colloidal quantum dots (QDs) of CdS, ZnS, and the ternary chalcogenide Cd1−xZnxS were synthesized by a nanoemulsion method, using a sonication probe as shearing power source. Quantum dots with diameters between 4 and 5 nm and cubic crystal structure were obtained and measured by HRTEM and XRD. In all cases, homogeneous solid solutions were obtained, as revealed by Vegard's Law, except with Cd0.39Zn0.61S. Optical properties of colloidal QDs were measured; the absorption edge is blue shifted, as the content of Zn increases, and showed a quantum confinement. Different emitted colors under UV light was observed, from dark brown with CdS to deep blue with ZnS. QDs of Cd0.39Zn0.61S show a white photoluminescence. Photoluminescence of the colloidal QDs is due to the combination of the direct band emissions and the trap emissions.