Mechanism for excitation-dependent photoluminescence from graphene quantum dots and other graphene oxide derivates: consensus, debates and challenges

Abstract

Luminescent nanomaterials, with wide applications in biosensing, bioimaging, illumination and display techniques, have been consistently garnering enormous research attention. In particular, those with wavelength-controllable emissions could be highly beneficial. Carbon nanostructures, including graphene quantum dots (GQDs) and other graphene oxide derivates (GODs), with excitation-dependent photoluminescence (PL), which means their fluorescence color could be tuned simply by changing the excitation wavelength, have attracted lots of interest. However the intrinsic mechanism for the excitation-dependent PL is still obscure and fiercely debated presently. In this review, we attempt to summarize the latest efforts to explore the mechanism, including the quantum confinement effect, surface traps model, giant red-edge effect, edge states model and electronegativity of heteroatom model, as well as the newly developed synergistic model, to seek some clues to unravel the mechanism. Meanwhile the controversial difficulties for each model are further discussed. Besides this, the challenges and potential influences of the synthetic methodology and development of the materials are illustrated extensively to elicit more thought and constructive attempts toward their application.

Synthesis and Characterization of Dual-Sensitive Fluorescent Nanogels for Enhancing Drug Delivery and Tracking Intracellular Drug Delivery

“…In addition, similarly to the excitation-dependent fluorescence properties of carbon quantum dots, polymer dots, and other fluorescent NPs, those of bAPSC NPs were observed to be consistent with their emission spectra [33,34,35]. Although the exact mechanism remains unclear, different organic fluorescent NPs have shown similar behavior [30,32,33,36,37]. Sun et al reported that polymer dots based on a PEI–polylactic acid (PLA) copolymer showed excitation-dependent fluorescence behavior with a significant redshift [30].…”

Carbon Quantum Dots: A Safe Tool to Learn about Quantum Phenomenon in Nanomaterials

“…As it can be seen, a wavelength-dependent behavior was found. According to the literature, this can be related to the NPs size [51] and/or energy traps created by surface groups [52]. Thus, the demonstration of quantum phenomenon is not an easy task to be performed in a simple lab experiment.…”

Effect of an anionic surfactant (SDS) on the photoluminescence of graphene oxide (GO) in acidic and alkaline medium

“…17 Teng and co-workers have also found such excitation wavelength independent photoluminescence of GO. 50 According to Gan et al, 51 giant red edge effect may be one of the origin of excitation wavelength dependent photoluminescence of GO quantum dots. But, such observation is absent in the GO, synthesized by us, because of different characteristics with respect to GO quantum dots.…”