ACS Nano 6, 8203 (2012)
For the application of graphene quantum dots (GQDs) to optoelectronic nanodevices, it is of critical importance to understand the mechanisms which result in novel phenomena of their light absorption/emission. Here, we present size-dependent shape/edge-state variations of GQDs and visible photoluminescence (PL) showing anomalous size dependences. With varying the average size (da) of GQDs from 5 to 35 nm, the peak energy of the absorption spectra monotonically decreases, whilst that of the visible PL spectra unusually shows non-monotonic behaviors having a minimum at da = ~17 nm. The PL behaviors can be attributed to the novel feature of GQDs, i.e., the circular-to-polygonal-shape and corresponding edge-state variations of GQDs at da = ~17 nm as the GQD size increases, as demonstrated by high-resolution transmission electron microscopy.
KEYWORDS.
Graphene · quantum dot · size · shape · edge · photoluminescence