Synthesis and Optical Characterization of Colloidal CdSe Quantum Dots Nucleated for A Long Time at High Temperature

Colloidal CdSe quantum dots were nucleated at about 300oC for 15 s and growth at 272oC up to 245 min in non-coordinating solvent octadecene by using hot-injection technique. Stearic acid was used as a capping agent in the synthesis of CdSe quantum dots. The nucleation time used in this study was considerably longer than those in the literature and its effect on the optical properties was examined. The first excitonic absorption and corresponding recombination peaks were observed in their optical absorption and photoluminescence spectra, respectively. The value of Stokes shift changed up to 70 meV. A peak and shoulder structure was obtained in the optical absorption and photoluminescence spectra of the sample growth for 20 min. It was indicated that CdSe quantum dots which are nucleated at high temperature for a sufficiently long period may have double size distribution. The images of CdSe quantum dots were obtained via transmission electron microscopy. Their images were processed with the image processing program ImageJ. The average size of CdSe quantum dots growth for 12 min was found as 2.63 nm. The size dispersion increased 4.6 times with respect to that of the monodisperse quantum dots. The X-ray energy transition peaks belong to Cd and Se elements were observed in their energy dispersive X-ray spectra. Symmetric and asymmetric vibrational modes of stearic acid molecules capping these quantum dots were determined at about 2848 cm-1 and 2914 cm-1 , respectively, by using Fourier transform infrared spectroscopy