One-pot synthesis of gradient interface quaternary ZnCdSSe quantum dots

Quantum dots (QDs) are capable of controlling the emission and absorption wavelength due to the bandgap widening effect of nanometer-sized particles. Many efforts have been made to increase the efficiency of QDs by using a core/shell structure. However, the conventional method of creating the core followed by shelling has the disadvantage of repeated processing. In this study, we synthesize composition gradient quaternary ZnCdSSe QDs of high efficiency (quantum yield = 88.96%, full width at half maximum = 28.20 nm) through one-pot synthesis. The X-ray diffraction peak for the (111) plane in ZnCdSSe QDs was shifted 2.64° compared to that for pure CdSe. From Cs-corrected STEM-EDS line scan results, it can be seen that the center of the QDs consists for more than 40% of Cd, clearly showing that a CdSe-rich core was formed, while the amount of Zn increases significantly toward the outer area. In addition, by using thermodynamics simulation, we propose a mechanism for formation of the composition gradient in QDs using one-pot synthesis and how this can be achieved with other compositions. Finally, we confirmed the chemical composition gradient inside a single quantum dot and proposed the formation behavior thereof using results of the thermodynamics simulation. The results herein may provide a way to identify the one-pot synthesis mechanism for quantum dots of various other composition gradients. This method greatly simplifies the procedure for synthesizing composition gradient ZnCdSSe QDs.