Characteristic electric-field manipulation of the optical response in monolayer graphene oxide

The flourishing research on graphene oxide (GO)-based optical sensing platforms, laser media, and optoelectronic devices calls for efficient, reversible, and spatially resolved methods to acquire and control multimodal optical information from GO. Here, we demonstrate that the optical transmission and fluorescence of monolayer GO (mGO)—two complementary optical readouts—can be reversibly manipulated by an external electric field (EEF) as low as ±1 kV/mm; the dual-channel optical responses are monitored simultaneously by a home-built scanning confocal microscope with a spatial resolution of about 300 nm, yielding spatially resolved, real-time multimodal optical information from every probed spot. Domain-resolved dual-channel imaging reveals that the absorption and emission of mGO are spatially heterogeneous and, more strikingly, that adjacent domains on a single mGO flake respond to the EEF in opposite directions: the transmission of one domain increases by more than 25% while its fluorescence is quenched almost completely, whereas the neighboring domain exhibits a ∼25% decrease in transmission together with a twofold fluorescence enhancement. We further define, for each probing spot, a characteristic electric field E c —the smallest field at which the transmission or fluorescence departs from its zero-field baseline by more than three standard deviations of the baseline noise. It varies from spot to spot (0.5–0.8 kV/mm) and correlates with the spectral profiles, converting the spatial heterogeneity of mGO into a quantifiable optical parameter. The changes recover completely upon field removal and remain reversible for more than 1 hour under periodically swept fields, without hysteresis or cumulative drift—consistent with a purely physical, electrochemistry-free modulation and substantially longer than the minute-scale reversibility of multilayer GO, a prerequisite for continuously operating sensing elements. These features make mGO a promising low-field, deeply modulated, and spatially programmable optical medium for electrically tunable optical sensors, fluorescence-based sensing, laser absorbers, and optoelectronic devices.