Size-dependent radiative decay processes in graphene quantum dots

Abstract

Radiative decay processes have been studied in graphene quantum dots (GQDs) by varying their size. The photoluminescence (PL) decay traces are well fitted to a biexponential function with lifetimes of tau(1) and tau(2), indicating their fast and slow components, respectively. The tau(1) is almost constant, irrespective of the average GQD size (d(a)) for two excitation wavelengths of 305 and 356 nm. In contrast, the tau(2) decreases as d(a) increases for d(a) <= similar to 17 nm, but d(a) > similar to 17 nm, it increases with increasing d(a) for both the excitation wavelengths, similar to the size-dependent behaviors of the time-integrated PL peak energy. We propose that the tau(1) and tau(2) originate from size-independent fast band-to-band transition and size-dependent slow transition resulting from the edge-state variation at the periphery of GQDs, respectively. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4760269]