Abstract

There is now a substantial body of data on the intermittent fluorescence of quantum dots (QD), such as CdSe.¹ Among the effects studied are the power law for the fluorescence “on times” (light periods) that evolves into an exponential decay under most but not all conditions, the power law for the “off” times (dark periods), typical values of the power, the effect of incident intensity and wavelength exciting the QD, including the effect of excitation near the band gap edge, the effect of temperature and of coatings, the observation of an infrared transition during the dark state, spectral diffusion and its scaling with intensity at low temperatures, the complementary nature of ensemble and single molecule experiments of QDs, and the experimental confirmation of a theoretically predicted change in power of the power law at short times² Nevertheless, in spite of the large body of data now available some experiments are one of a kind, and so their generality isn't established, and other desired experiments appear to be not yet performed. We discuss the interaction between experiment and a reaction-diffusion electron transfer theory. In the latter the dark state can be formed by an Auger–induced electron transfer from a surface state (perhaps a dangling Se⁻² ion) to a hole in the valence band created by a photo-excitation. Existing puzzles and missing data will be pointed out. In any potential use of QDs or nanorods for solar energy conversion³ the latter can be helped by understanding the factors affecting fluorescence and other undesirable alternative fates of the excitation energy.

© 2009 APS DLS