Core/shell quantum dots (QDs) with maximal photoluminescence quantum yields are necessary for modern nanotechnological applications. Shell plays the key role in optical and chemical properties of QDs: properly selected high band gap semiconductor material increases the photoluminescence quantum yield (PL QY) and provides sufficient protection of the core from the environment. Yet, the shell structures such as ZnS or CdS/ZnS still have their own shortcomings and typically don’t allow to obtain QDs with the maximal quantum yield.
We propose a new structure of ZnS/CdS/ZnS shells on wurtzite CdSe QD cores. This structure provides strong charge carrier localization and sufficient shell thickness which creates reliable protection from the environment. The first monolayer-thick ZnS shell gives the highest potential barrier for electron–hole pairs, thereby maximizing emission outcome. The second CdS shell separates two neighboring monolayers of ZnS, increasing the shell thickness. The last ZnS shell creates the additional potential barrier and is compatible with common surface ligand exchange protocols. The QDs obtained using this approach have PL QY close to 100%.