Effect of Zn/Cd Molar Ratio on Characteristics of Homogeneously Alloyed Zn x Cd1-x S Nanocrystals

Homogeneously alloyed Zn (x) Cd1-x S nanocrystals (NCs) with varying Zn/Cd molar ratio have been prepared by a colloidal chemical method. Alternating injection of small amounts of Zn and Cd precursor solution was proposed and applied to reduce the preparation temperature. The morphology, size, crystal structure, composition, particle concentration, optical absorption, and photoluminescence (PL) characteristics of the samples were investigated by using transmission electron microscopy (TEM), x-ray diffraction (XRD) analysis, energy-dispersive x-ray spectroscopy (EDX), atomic absorption spectroscopy (AAS), ultraviolet-visible (UV-Vis) absorption, and PL spectroscopy. The results show that the Zn/Cd molar ratio strongly affected the size, fraction of crystal phases, and optical bandgap energy of the Zn (x) Cd1-x S NCs. The increase in the particle size with decreasing Zn/Cd molar ratio was analyzed based on the concentration of stearic acid (SA) in the reaction solution and the chemical reactivity of the Zn and Cd precursors. The relationship between the optical bandgap energy and composition of the ternary NCs obeys a theoretical model proposed for the regime with weak quantum confinement.