Deep Ultraviolet Photoluminescence of Water-Soluble Self-Passivated Graphene Quantum Dots

TLDR

Carbon‑based quantum dots typically show excitation‑wavelength dependent photoluminescence, a behavior also observed in these GQDs. The GQDs were synthesized from glucose via a simple microwave‑assisted hydrothermal process, yielding crystalline particles about 1.65 nm in diameter. The resulting GQDs emit deep‑ultraviolet light at 4.1 eV—the shortest wavelength among solution‑based quantum dots—independently of particle size, with 7–11 % quantum yield, and can convert blue LED light into white light, a behavior attributed to a self‑passivated surface layer.

Abstract

Glucose-derived water-soluble crystalline graphene quantum dots (GQDs) with an average diameter as small as 1.65 nm (∼5 layers) were prepared by a facile microwave-assisted hydrothermal method. The GQDs exhibits deep ultraviolet (DUV) emission of 4.1 eV, which is the shortest emission wavelength among all the solution-based QDs. The GQDs exhibit typical excitation wavelength-dependent properties as expected in carbon-based quantum dots. However, the emission wavelength is independent of the size of the GQDs. The unique optical properties of the GQDs are attributed to the self-passivated layer on the surface of the GQDs as revealed by electron energy loss spectroscopy. The photoluminescence quantum yields of the GQDs were determined to be 7-11%. The GQDs are capable of converting blue light into white light when the GQDs are coated onto a blue light emitting diode.