Multi Emissive Graphene Oxide Quantum Dots Showing Remarkable pH Responsive Long Wavelength Emission

Abstract

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