Sodium-Citrate-Assisted Synthesis of Aqueous CdTe Nanocrystals: Giving New Insight into the Effect of Ligand Shell

We report a protocol for investigating the effect of the ligand shell in the growth process of aqueous CdTe nanocrystals (NCs) from the viewpoint of both experiment and theoretical calculation. Experimentally we develop a new method of sodium-citrate-assisted preparation of aqueous CdTe NCs, which breaks through the restriction of thiol/Cd ratio (1.2:1) in conventional aqueous synthesis and realizes the extensive tunability of the thiol/Cd ratios from 0.1:1 to 2.4:1. On the basis of the investigation of CdTe NCs in the presence of sodium citrate (SC), the ligand shell is confirmed to control both the growth rates and the photoluminescence quantum yields (PL QYs) of aqueous NCs. Theoretically, according to the absolute rate theory (ART), the growth rates of NCs are determined by the reaction temperature, activation energy, and concentration of Te. Theoretical simulation of the NC growth process by MP2/Lanl2DZ in the Gaussian 03 program indicates that the nature of the ligand shell greatly affects the activation energy of NCs through formation of the transition-state complex, thus affecting the growth rates of NCs. Obviously, both experiment results and theoretical calculation prove that the nature of the ligand shell plays a key role in the growth process and PL QYs of aqueous CdTe NCs.