Growth mechanism of hydrophilic CdTe nanocrystals with green to dark red emission

A modified method has been developed to fabricate high-quality CdTe nanocrystals (NCs) with a tunable photoluminescence (PL) range between green and dark red using thioglycolic acid (TGA). Namely, CdTe NCs with dark red emission (PL peak wavelength of 672 nm) and a PL quantum yield (QY) of 46% were created by controlling the NC growth kinetics. The molar ratio of TGA/Cd2+ in solutions and the concentration of starting materials play important roles in creating the NCs with a large size for long PL peak wavelength and decreased surface defects for a target of a high PLQY. Lifetime measurement indicated that the average lifetime of the NCs decreased at the beginning of a reflux and then converted to increase with time. This means that long reflux time resulted in a CdS-like shell formed on CdTe NCs. The X-ray diffraction analysis of the NCs illustrated that CdS-like layer were created on CdTe NCs, in which S(2-) ions generated by the decomposition of TGA during a long reflux period.