The photoluminescence of step-wise reduced graphene oxide quantum dots

Abstract

Graphene oxide quantum dots (GOQDs) were synthesized by liquid-phase oxidation using the mixture of HNO3 and H2SO4. These GOQDs showed blue-green photoluminescence (PL), and a dual-wavelength emission. The emission peak could be distinguished as two peaks located at 463 nm and 496 nm. The GOQDs were further step-wise reduced using different amount of hydrazine to obtain reduced quantum dots (RQDs). The content and type of oxygen-containing functional groups varied with the reduction degree. For the same sample, the PL emission peaks exhibited independence on the excitation wavelength, revealing that the samples we prepared possessed a certain energy band structure. The PL of the GOQDs could be tailored through varying the reduction degree by changing the amount of hydrazine. The 463 nm emission peaks of the RQDs blue-shifted, while the 496 nm emission peaks red-shifted along with reduction degree. The PL intensities of the RQDs decreased drastically compared with that of the GOQDs. Based on these results, we proposed that the short wavelength emission peak was originated from oxygen-bearing groups, while the long wavelength emission peak was originated from sp2 domains of the GOQDs. Our work could help for the understanding of the PL behavior and mechanism of graphene-based quantum dots.