Modern technological applications of photoluminescent (PL) semiconductor nanocrystals or quantum dots (QDs) require not only the top optical qualities like 100% PL quantum yield, but also high unity in size, shape and structure through the whole nanocrystal ensemble. These parameters are also of high importance for large-scale and high-throughput manufacturing of these nanomaterials. Nowadays, plenty of methods for production of monodisperse CdSe QD cores exist, yet there is still urgent need for development of reliable procedure for deposition of uniform high band gap shell, which confines charge carriers in luminescent QD cores and protects it from the environment.
Here, we demonstrate how modelling of QD structure and QD growth mechanism may aid the development of an advanced methodology for precise layer-by-layer (L-b-L) shell coating procedure. The structural models are based on crystallographic parameters of respective QD material, and allow one to inspect and follow the formation of the nanocrystal in the L-b-L manner. Quantitative data extracted from these structural models, namely the exact quantity of materials needed for the formation of single shell layer, can be readily used in the design of shell coating procedure. Our novel approach was practically implemented in a series of experimental works. Thus, we were able to predict the evolution of the position of the first excitonic transition in absorbance spectra (and, therefore, the nanocrystal size) during the overgrowth of wurtzite CdSe core nanocrystals, to demonstrate the L-b-L coating of CdSe nanorods with a ZnS shell, and finally to synthesize the novel CdSe/ZnS/CdS/ZnS core-multishell QDs, which have almost 100% PL QY.