Reduction and Quantum Confinement Effects in Graphene Oxide: Relevance for Electro-optical Applications

Graphene oxide offers opportunities in electro-optical applications owing to its tunable absorbance and emission gamut. Particularly, graphene oxide nanosheets (GO-n) prepared via laser reduction represent a peculiar scenario where optical properties are influenced by factors encompassing chemical reduction, pore formation, and quantum confinement. The disentanglement of these in modifying absorbance and photoluminescence spectra is challenging but provides insights for tailoring GO-n optics. We tackle this issue by performing density functional theory simulations. We prepare graphene oxide nanosheets via nanosecond-multipulsed laser reduction and carry out compositional, morphological, and optical characterization. With simulations, we first span across a wide landscape of structures, representing laser-induced reduction and confinement scenarios, and finally, we achieve a quantitative reproduction of absorption spectra, enabling the disentanglement of the mentioned influences. We discover that internal quantum confinement, which intensifies with higher laser energy densities, dominates the optical properties. Specifically, low energy densities promote pore formation, while higher energy densities lead to internal quantum confinement. Our study guides the fine-tuning of graphene oxide nanosheets concerning both material absorption and luminescence. Reduction enhances absorption and photoluminescence in the visible and near-infrared regions, while internal quantum confinement can boost or diminish absorption in the visible spectra, simultaneously boosting photoluminescence in the blue-violet and green ranges.