Precursor ratio engineering for tunable growth kinetics and surface passivation in CdSe quantum dots

Quantum dots (QDs) are promising materials for use in optoelectronic, photovoltaic, and bioimaging applications since their size-dependent properties are tunable. Among their synthesis parameters, the precursor ratio strongly influences their nucleation, growth dynamics, and surface chemistry. In this study, we investigated the effect of the Cd:Se ratio (7:1, 1:1, and 1:7) on the optical properties and growth dynamics of CdSe QDs. Absorption and photoluminescence (PL) spectra showed a redshift with increasing reaction time, indicating particle growth and a lower bandgap. Estimations of the QD size on the basis of the effective mass approximation supported these trends and thereby confirmed the size dependence of the optical behavior of the QDs. X-ray photoelectron spectroscopy spectra also confirmed that the surface components of CdSe QDs varied with changing Cd:Se ratios. Time-resolved PL measurements showed that Cd-rich QDs had longer carrier lifetimes, which could be attributed to improved surface passivation and stronger quantum confinement, while Se-rich QDs had shorter carrier lifetimes, possibly because of more surface defects and nonradiative recombination. These results highlight the importance of the precursor ratio, especially a Cd-rich condition, in controlling the QD quality and optimizing the QD performance for use in optoelectronic applications.