Femtosecond dynamics of CdTe quantum dots in water

We present studies on femtosecond to nanosecond fluorescence dynamics of aqueous solutions of cadmium telluride (CdTe) quantum dots (QDs) with diameters of 3.1 and 3.6 nm. Ultrafast times in the range 200–320 fs and 1.6 ps were determined, and assigned to electron relaxation to the bottom of the conduction band and to recombination of trapped electrons and holes. These times are common to the relaxation mechanisms of QDs in solution, and therefore suggests that intrinsic mechanisms for electron and hole relaxation dominate over surface effects, in agreement with other reports. Additionally, times of ∼40 ps, ∼600 ps and ∼20 ns due to radiative transitions were recorded. These results are relevant to understanding the photodynamics of CdTe and other QDs in water which should play a fundamental role in their signal when used in biological media.