Structure and optical properties of capped and uncapped CdS nanoparticles prepared in aqueous medium

摘要

We have prepared the hexagonal structure of CdS nanoparticles in an aqueous solution with different sizes and varied surface compositions by using fixed molar ratio of the starting precursors in the presence of capping molecules. In addition, we have prepared uncapped CdS nanoparticles by cadmium chloride and thiourea at low temperature. We showed that the environmental conditions and the type of the aqueous medium are the effective parameters for the exchange of the nanoparticle size. The prepared nanoparticles have sizes in the range from 25 to 100 A. We have compared the experimentally determined size of CdS nanoparticles with that determined by theoretical calculations. The comparison showed that the size determined by Scherrer's equation is fitted well with the empirical tight binding calculations, and that the effective mass approximation yields size values is in good agreement with the size estimated by high resolution transmission electron microscopy. Photoluminescence spectroscopy revealed that the nanoparticles with stoichiometries composition S/Cd ～ 1 have a high intensity band edge emission in the blue region for the capped nanoparticles and green emission for the uncapped nanoparticles.