Size controllable preparation of graphitic quantum dots and their photoluminescence behavior

To control the size of graphitic quantum dots (GQDs), an electrochemical method was successfully developed with applied potentials cycling between −5.0 and 5.0V at various scan rates from 0.2 to 0.5V/s. The average size of the resultant GQDs decreases from 12 to 3.4nm with increasing scan rates, as verified by their transmission electron microstructure (TEM) images. The X-ray diffraction (XRD), optical absorption, photoluminescence (PL), Fourier Transform Infrared (FTIR) and photoluminescence excitation (PLE) behaviors of those GQDs were investigated. The result shows that the n–π* electronic transition resulting from the surface oxygen groups contributes to the PL emission, besides the π–π* electronic transition due to their sizes.