Multi-emissive graphene oxide quantum dots with remarkable pH-responsive long-wavelength emission

The present work reports the preparation of graphene oxide quantum dots (GOQDs) via oxidative cutting from GO nanosheets under relatively controlled conditions. The aqueous solution of GOQDs exhibited remarkable pH dependence, where emissions under acidic or near-neutral conditions showed emission maxima in the green/yellow region. In contrast, an intense orange-red light emission (with a relative photoluminescence quantum yield of similar to 30%) was observed at pH 12.8. Under acidic or near-neutral conditions, H-bond led J-type aggregates were found as emissive bodies. However, under alkaline conditions, counterintuitive aggregations between negatively charged GOQD particles were observed to occur via donor-acceptor interactions between suitable surface functional groups. A remarkable quenching of the orange-red emission signal (at pH 12.8) owing to cation-induced aggregation of the emissive aggregates was observed in the presence of externally added electrolytes. A PVA-GOQD film (pH 2, photoluminescence quantum yield = 37.8%), when casted over a UV chip of 390 nm, emitted appreciable pure white light with a CIE index of (0.336, 0.388), a color rendering index (CRI) of 85, and a correlated color temperature (CCT) of 5160 K. The PVA-GOQD films/gels demonstrated appreciable photostability under sunlight and UV radiation, highlighting their potential application as photoemissive layers in LEDs.