Abstract
To explore aggregate-induced emission (AIE) properties, this study adopts a one-pot hydrothermal route for synthesizing polyethylene glycol (PEG)-coated graphene quantum dot (GQD) clusters, enabling the emission of highly intense photoluminescence under blue light illumination. The hydrothermal synthesis was performed at 300 °C using o-phenylenediamine as the nitrogen and carbon sources in the presence of PEG. Three different solvents, propylene glycol methyl ether acetate (PGMEA), ethanol, and water, were used for dispersing the PEG-coated GQDs, where extremely high fluorescent emission was achieved at 530–550 nm. It was shown that the quantum yield (QY) of PEG-coated GQD suspensions is strongly dependent on the solvent type. The pristine GQD suspension tends to be quenched (i.e., QY: ~1%) when dispersed in PGMEA (aggregation-caused quenching). However, coating GQD nanoparticles with polyethylene glycol results in substantial enhancement of the quantum yield. When investigating the photoluminescence emission from PEG-coated GQD clusters, the surface tension of the solvents was within the range of from 26.9 to 46.0 mN/m. This critical index can be tuned for assessing the transition point needed to activate the AIE mechanism which ultimately boosts the fluorescence intensity. The one-pot hydrothermal route established in this study can be adopted to engineer PEG-coated GQD clusters with solid-state PL emission capabilities, which are needed for next-generation optical, bio-sensing, and energy storage/conversion devices.
Highlights
Graphene quantum dots (GQDs) have experienced a surge in attention compared to other nanomaterials thanks to their superior physicochemical properties including excellent solubility, high stability, and low toxicity [1]
Low quantum yield (QY), wide full width at half maximum (FWHM), and solvent-dependent PL behavior are among the major issues yet to be addressed
The latter plays a crucial role in affecting the PL behavior of GQD suspensions such as red/blue shift, FWHM, and QY, mainly originating from its dispersion extent and storage period in various solvents
Summary
Graphene quantum dots (GQDs) have experienced a surge in attention compared to other nanomaterials thanks to their superior physicochemical properties including excellent solubility, high stability, and low toxicity [1]. Nanomaterials 2021, 11, 1383 such as remarkable biocompatibility, very robust interfacial structure, high solubility (aqueous), and a tunable band gap [11,14]. Despite these remarkable attributes, the widespread adoption of GQDs faces several critical challenges. Low quantum yield (QY), wide full width at half maximum (FWHM), and solvent-dependent PL behavior are among the major issues yet to be addressed. The latter plays a crucial role in affecting the PL behavior of GQD suspensions such as red/blue shift, FWHM, and QY, mainly originating from its dispersion extent and storage period in various solvents.
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