Synthesis of white-light-emitting graphene quantum dots via a one-step reduction and their interfacial characteristics-dependent luminescence properties
Graphene quantum dots (GQDs) have attracted great attention because of their possible applications in various fields. Here we report a facile one-step method for the fabrication of a type of white-light-emitting GQD (W-GQD) by NaBH4 reduction. The highly-pure white-light emission of the obtained W-GQDs was confirmed by calculating the Commission International de l’Éclairage (CIE) 1931 chromaticity parameters (x = 0.30, 0.36) from the fluorescence luminescence data. We observed an important increase in the absolute quantum yield from 0.20% to 3.62% before and after the chemical reduction. The influence of the interface characteristics on the emission properties was analyzed by UV-vis, Fourier transform infrared, and X-ray photoelectron spectroscopies. The results illustrated that the carboxyl and epoxy groups were reduced into hydroxyl groups and that the five- and six-membered lactol groups transformed into aromatic carboxylic acid and hydroxyl groups. The chemical modifications enhanced the electron density of the π structure and also suppressed the non-radiative recombination, resulting in a bright white-light emission. Furthermore, the as-prepared W-GQDs were successfully utilized for the fabrication of a white-light-emitting diode.