One-step preparation of N, S-doped graphene quantum dots for white light-emitting diodes

Abstract

Two-dimensional (2D) materials consist of either a single layer or just a few layers of atoms or molecular layers, and their exceptional optoelectronic properties including high carrier mobility, wide spectral absorption range, and optical response from the number of layers. Graphene quantum dots (GQDs) as a small-sized 2D material exhibited unique physical and chemical properties at the quantum scale. In this study, the N, S-doped GQDs (named as Y-GQDs) were synthesized through straightforward solvothermal process using 2, 2-dithiobenzoic acid and o-phenylenediamine as the precursors. The distribution of the prepared GQDs sample was uniform, with height varying between 0.6 and 0.8 nm. The excellent optical properties of Y-GQDs were attributed to the high crystalline graphene structure and rich functional groups including -C-SO₃-C-, -C-SO₄-C-, C-N, etc. The optimal excitation and emission wavelengths of Y-GQDs were 380 nm and 535 nm, respectively. Additionally, the multi-color and tunable luminescence characteristics could be achieved by excitation wavelength, solvent, and concentration. Gratifyingly, the N, S-doped GQDs were successfully used to build white light emitting devices via a sol-gel process. The color rendering index reached 83.7 with color temperature of 5306 K, and the GQDs exhibited good optical stability under different driving currents and UV light. This study underscored the significant potential of GQDs in creating promising phosphors for superior lighting applications.