Synthesis of highly stable dihydrolipoic acid capped water-soluble CdTe nanocrystals

To prevent the dissociation of organic ligands from the inorganic core and accordingly enhance colloidal stability, is the prerequisite for the further application of nanocrystals in different areas. Dihydrolipoic acid (DHLA) appears very promising for the stabilization and the further functionalization of CdTe nanocrystals because DHLA is characterized by a carboxylic acid group and two thiol functions, through which simultaneous anchorage onto a nanoparticle's surface is possible. For the first time, we synthesized highly luminescent CdTe nanocrystals (maximum quantum yield of 42%) in aqueous solution by the reaction of Cd2+ and NaHTe using DHLA as capping reagent. The influence of various experimental variables, including reaction temperature, ligand-to-Cd ratio and pH value as well as Te-to-Cd ratio, on the growth rate and optical properties of the obtained CdTe nanocrystals have been systematically investigated. Furthermore, the stability of the dithiol DHLA capped CdTe nanocrystals was compared with the monothiol ligands thioglycolicacid (TGA) and mercaptopropionic acid (MPA) capped nanocrystals. Experimental results indicate that the DHLA capped nanoparticles show better chemical and thermal stability than those capped by TGA or MPA. The mechanism for the high-quality optical properties and the good stability of the resulting CdTe nanocrystals is also primarily elucidated.