Size Control at Maximum Yield and Growth Kinetics of Colloidal II-VI Semiconductor Nanocrystals

We investigated the growth kinetics of CdSe nanocrystals for a hot-injection colloidal synthesis, as a function of selected key process parameters. In this investigation, the synthesis consisted in the injection of trioctylphosphine-selenium into cadmium oleate, followed by nucleation and growth stages. The evolution of size and size distribution of the nanocrystals was monitored during the synthesis via UV–visible absorption and photoluminescence spectroscopy. Three growth parameters have been extracted from the experimental data through a general kinetic growth model, and discussed: the initial particle size, the growth rate, and the particle size at the end of the growth. A modification of the classical nucleation theory has been developed to explain and predict the equilibrium (final) size of the nanoparticles, by taking into consideration the consumption of monomers during crystal formation and growth. The model accurately predicts the trends of the crystal size as a function of the oleic acid concentration. The model represents a valuable tool for the study of colloidal crystal growth providing new insight into the physical and chemical processes behind the nucleation and growth. Moreover, it enables exploration of new limits in terms of typical synthetic conditions, aiming at the optimization of the synthesis yield for every single case at hand—a very important goal in view of the ever-growing need for large-scale fabrication of colloidal nanostructures.