Fluorescence lifetime and blinking of individual semiconductor nanocrystals on graphene

A new class of optoelectronic nanodevices consisting of 0D semiconductor nanocrystals and 2D single graphene layers is attracting much attention. In particular, such a system may be used to investigate and control the transfer of energy and charge in low-dimensional systems. To this end, the fluorescence dynamics of individual colloidal quantum dots (QDs) on graphene are investigated on both the 10^-9-10^-8 s time scale (fluorescence lifetime) and the 10⁰-10² s time scale (blinking statistics) in this paper. We find that (i) a nonradiative energy transfer rate of ≈5 × 10⁸ s^-1 is obtained from the reduced lifetimes of QDs on graphene as opposed to those on insulating substrates such as glass; (ii) QDs still exhibit fluorescence intermittency (" blinking") on graphene; (iii) the cumulative distribution functions of the "off" times may be described by power-law statistics; (iv) QD coupling to graphene increases the time spent in the "on" state while the time spent in the "off" state remains relatively unchanged; and (v) the fluorescence emission spectrum of the QDs is practically unaltered by the QD-graphene coupling.