Tuning Optical Properties of High Quantum Yield Nitrogen Doped Graphene Quantum Dots Synthesized by Pulsed LASER Ablation

The graphene quantum dots (GQDs) have attracted the attention of researchers due to their excellent properties and potential applications in biomedicines, energy storage devices, and photovoltaics. The photoluminescence is one of the most important characteristics of GQDs. The doping of GQDs with nitrogen atoms is one of the most effective ways to tune their photoluminescence emission and increase quantum yield. In this work, high-quality nitrogen-doped graphene quantum dots (N-GQDs) were synthesized by using the pulsed laser synthesis method at various irradiation powers of the pulsed laser and changing the concentration of nitrogen doping to effectively tune the photoluminescence emission and improve the quantum yield (QY) of the as-synthesized N-GQDs. The TEM, HRTEM, XPS, XRD, Raman spectroscopy, and FTIR were carried out to observe the morphology, size distribution, crystalline structure, and to prove successful doping of GQDs with nitrogen atoms. To observe the optical properties of the as-synthesized N-GQDs, UV-vis and photoluminescence measurements were carried out. The as-synthesized NGQDs exhibit a high-quality crystalline structure of graphene. A high quantum yield was exhibited by the obtained N-GQDs as compared to the pristine GQDs. The obtained N-GQDs with oxygen-rich functional groups exhibit a strong emission. This work may be helpful to expand the scope of GQDs, especially in biomedical applications.