Effects of Size and Capping Reagents on Biexciton Auger Recombination Dynamics of CdTe Quantum Dots

CdTe quantum dots (QDs) were synthesized using oleic acid (OA) and thioglycolic acid (HS-CH2COOH, TGA) as capping reagents. Biexciton Auger recombination of CdTe QDs was examined by femtosecond transient absorption spectroscopy by changing excitation intensity. The lifetime of biexciton Auger recombination tau(Auger) was analyzed as a function of QD diameter D and capping reagents. It was found that tau(Auger) is proportional to D-alpha, and that the scaling index alpha is dependent on capping reagents and/or surface conditions. For TGA capped CdTe QDs, alpha is determined to be 4.6, whereas it is 7.0 for OA capped CdTe QDs with high luminescence quantum yields Phi of 60-85%. This relationship did not hold for small size OA capped CdTe QDs with rather low (1) of 15-30%, in which tau(Auger) became as short as 2 similar to 3 ps irrespective of the diameter. These results suggest that biexciton Auger recombination of CdTe QDs is strongly dependent on the QD surface trapping and capping reagents.