Formation of "Steady Size" State for Accurate Size Control of CdSe and CdS Quantum Dots

We report on the formation of a "steady size" state for the growth of CdSe and CdS quantum dots (QDs), in which the size of the QDs remains constant and independent of reaction time. Kinetic study reveals that this state exists only when certain coordinating ligands are within a range between N_S and N_V + N_S. N_S and N_V represent the number of atoms on the surface of the QDs and the total amount of atoms in the QDs, respectively. Under this condition, the size R of the QDs can be controlled solely by the reaction temperature T with a relationship of 1/R² ∼ T. More importantly, a highly reproducible and accurate linear control of the emission wavelength of QDs on a subnanometer scale by the reaction temperature is achieved. The discovery enables large-scale synthesis of QDs with minimum size variation that meets critical demands on wavelength accuracy for QD-based optoelectronic applications.