Effects of ligand molar ratio on optical properties of CdSe quantum dots

CdSe quantum dots (QDs) functionalized with a binary ligand system were prepared using the hot-injection strategy, and absorption and photoluminescence (PL) spectroscopy were used to investigate the optical properties of the resultant CdSe QDs prepared under different reaction parameters. A large redshift and spectral broadening were observed in the visible range of the absorbance and PL spectra with increasing reaction time and oleic acid ligand molar ratio as a result of the quantum size effect and rapid abnormal growth. The focusing-defocusing regime, which was attributed to the Ostwald ripening effect, was found to be independent of the ligand concentration and was usually dependent on the initial concentration of the monomer. A gradual decrease was observed in the full-width at half maximum (FWHM) of the PL peak for CdSe QDs prepared using different ligand molar ratios and with reaction times as long as 20 min because of increasing homogeneity; the FWHM values of the PL peak then increased after 20 min of reaction because of monomer depletion.