Investigating the role of polytypism in the growth of multi-shell CdSe/CdZnS quantum dots

In this work we investigate the role that polytypism has on the growth of multi-shelled, giant quantum dots (gQDs). Multi-shell growth was initiated at CdSe cores with either zinc blende or wurtzite crystal structures. The shells consisted of a Cd_xZn_1-xS gradient that was deposited in a slow layer-by-layer SILAR process. The final gQDs had sizes of >15 nm, with shapes and symmetry that were influenced by core type, and polytypic growth conditions. A study of morphology and crystal structure change at each stage of shell growth was carried out by powder XRD, TEM, and HRTEM, and the photophysical properties were studied by UV-vis and fluorescence spectroscopy. In both types of cores, shell growth was found to transition to wurtzite, whereas the percentage of polytypism was shown to alter both morphology and optical properties.