Temperature-sensitive growth kinetics and photoluminescence properties of CdS quantum dots

As a critical issue in green'' synthesis, the mechanism by which the growth temperature influences the photoluminescence (PL) properties of quantum dots (QDs) remains unclear. In this work, temperature sensitive growth kinetics and PL evolution of thioglycolic acid (TGA) capped CdS QDs were systematically investigated. This revealed that TGA capped CdS QDs coarsened below and above 90 degrees C experienced completely different growth kinetics, i.e. a two-stage growth from oriented attachment to Ostwald ripening (OA-OR) and a hybrid growth of the two mechanisms (OA + OR), respectively. With the evolution of the OA-OR growth, the corresponding PL shows characteristics of a gradual weakness of the defect-related emissions centered at similar to 650 nm and a steadily enhanced band-edge emission peaking at similar to 450-470 nm. For the OA + OR hybrid growth, the defect-related emission band steadily coexists with the band-edge emission after an initial decrease. In-depth kinetics and high-resolution transmission electron microscopy (HRTEM) investigation indicate that a low temperature favors a long-term OA self-integration stage, by which internal defects could be relaxed or even eliminated. For a high temperature, this tendency could be greatly inhibited by the concurrent OR growth just around these defects. The FTIR analysis further revealed that the adsorption-desorption equilibrium of capping ligands was temperature-sensitive, resulting in different growth kinetics and PL characteristics of CdS QDs.