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

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