Graphene Oxide Multilayers with Violet-Blue Luminescence Fabricated Through Controlled Oxidation at 275 K

Synthesis of multilayer graphene oxide (GO) was achieved through a Hummers method with meticulous control over the addition of the oxidizing agent. Precursors were immersed in an ice bath during the synthesis to maintain a temperature of approximately 275 K in oxidation stages I and II, temperature was measured with a thermocouple inside the cooling bath, in direct contact with the vacuum filter flask at the level of the reactants. In contrast to the variety of Hummers synthesis methods—where the system is maintained at certain temperature during the initial oxidation stage and heat continues to be supplied during the second stage—our setup operates at low temperature from the beginning to the conclusion of the process. A detailed analysis of the compositional, structural, and optical properties of the fabricated GO was conducted, revealing a notable photoluminescent band in the 380–480 nm region. This property is of interest for a potential future application in the field of optoelectronics. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed that the structure of the material consists of a sp3 matrix with sp2 domains. Raman spectroscopy revealed an ID/IG ratio of 2.7, which could indicate a high density of structural defects or extremely small sp2 graphitic domains. Furthermore, deconvolution of the 2D band suggests the presence of multilayers in the GO. Fourier transform infrared spectroscopy (FTIR) analysis revealed the presence of all functional groups associated with the GO. Upon observation of the photoluminescence exhibited by the material, a broadband centered on the violet-blue emission, with a possible mechanism consistent with the literature associated with the transitions between sp2 domains and localized states in the basal plane defects or it might be caused by quantum confinement effects. The diminished contribution from the green emission could be caused by the transitions between localized states sp2 and the functional groups associated with oxygen.