Size controllable preparation of graphitic quantum dots and their photoluminescence behavior

• Size controllable graphitic quantum dots were prepared via an electrochemical route.
• They show identical PL spectra at 445 nm on being excited by 360 nm.
• The PL emission originates from the surface oxygen groups rather than sizes.

To control the size of graphitic quantum dots (GQDs), an electrochemical method was successfully developed with applied potentials cycling between −5.0 and 5.0 V at various scan rates from 0.2 to 0.5 V/s. The average size of the resultant GQDs decreases from 12 to 3.4 nm 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.

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