Temporal evolution of optical absorption and emission spectra of thiol capped CdTe quantum dots

To understand the effect of end-groups of thiol-molecules on the structural, absorption, and photoluminescence (PL) properties, CdTe quantum dots (QDs) were synthesized with the capping of thioglycolic acid (TGA), mercaptoethylamine (MEA), l -cysteine ( l -Cys) and glutathione (GSH) in aqueous medium. The growth kinetics of the nanocrystals with the variation in the end-groups of thiols has also been spectroscopically investigated. The average sizes of the nanocrystals ranged from 2 to 5 nm, which is well within the quantum confinement regime. The size and phase purity of the QDs were determined by XRD and HRTEM. With respect to size-distribution, the temporal evolution of QDs was found to involve three stages, namely focusing, defocusing and equilibrium. Hydrodynamic sizes were also measured using DLS system. FTIR spectra revealed that the thiol end of the capping agent binds to the particle–surface while the carboxyl or amine group remain free. The multi-colour photoluminescence illustrated the excellent size-tunable optical properties of the QDs. Zeta-potential for TGA-capped CdTe QDs was measured to be − 45 mV, indicating high surface charge and hence greater colloidal stability. Such QDs are well suited for bioimaging and therapeutic applications.