In this study cadmium selenium quantum dots (CdSe QDs) were synthesized with different capping agents namely, l-cysteine, mercaptosuccinic acid and thioglycolic in aqueous solution. The effect of capping agent on the nucleation and particle growth process was investigated. Electronic absorption and emission fluorescence spectroscopy techniques were applied to map out the size evolution of the QDs. The methods of SEM, EDX, XRD and FTIR were also used for characterization of the prepared samples. The average diameters of the synthesized quantum dots were estimated using different methods. Results revealed that the order of particles size was obtained as follow: CdSe-MSA > CdSe-LCY > CdSe- TGA. Results also showed that the TGA has the strongest binding ability with the QDs surface; in contrast MSA has the weakest binding ability. Results indicated that there is a mutual relationship between changing the bandwidth and the rate of growing particle size of the quantum dot, so that the particles with slow growing rate (CdSe-TGA, 12 h) its bandwidth varies smoothly. Also the magnitude of bandwidth of the spectrum is fairly dependent to the size of the CdSe QDs during the growth process. The quantum dots with larger size (CdSe-MSA) have the fluorescence spectra with broader bandwidth. The trend of the particles growth was discussed in details. Results revealed that the kind of capping agents are considerably influence on the nucleation as well as particle growth processes.
