Size and Dopant Dependent Single Particle Fluorescence Properties of Graphene Quantum Dots

Abstract

The emissive properties of both doped and non-doped graphene quantum dots (GQDs) with sizes ranging from 3-11 nm were analyzed at the single particle level. Both doped and nondoped GQDs are a composite of particles exhibiting green, red, or NIR fluorescence on excitation at 488, 561, and 640 nm, respectively. Nitrogen doped GQDs (N-GQDs) with diameters ranging from 3.4 to 5.2 nm show a larger proportion of particles with NIR emission as compared to non-doped particles. and the fluorescence intermittency seen in single GQD particles. While ms to sec time scale blinking was regularly observed for red emitting non-doped GQDs, nitrogen doping significantly reduced blinking. Both doped and non-doped particles also exhibit moderate size dependent photophysical properties.

Fluorescence and Sensing Applications of Graphene Oxide and Graphene Quantum Dots: A Review

“…[9] Increasing the doping percentage of nitrogen in GQDs could red-shift the emission and improve the photostability. [10] Due to quantum confinement, changing the size of GQDs can modulate the electronic structure and thus can shift the fluorescence from green, red to NIR. In addition, change in the localized domains, where π-electrons are confined in localized sp 2 regions, can also alter fluorescence of GO.…”

“…In addition, change in the localized domains, where π-electrons are confined in localized sp 2 regions, can also alter fluorescence of GO. [10–11] …”

Smart Utilization of Carbon Dots in Semiconductor Photocatalysis

“…Commonly used CDs show PL at short wavelengths (blue or green region), with the emission caused by sp 2 clusters isolated by sp 3 networks in the CDs . CDs with longer PL emission wavelengths (yellow to near infrared region) have also been synthesized using special starting materials, via heteroatom‐doping, the creation of unique surface states, or careful separation . Supported by density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations, Mahasin et al demonstrated that the PL properties of graphene quantum dots (GQDs) can be tuned from deep UV to near infrared by modification of the particle size, shape, edge configuration, surface defects, surface functional groups, and heteroatom doping.…”

Recent Advances in Graphene Quantum Dots as Bioimaging Probes

“…Because of their low cost and easy availability, natural resources such as coffee grounds [100], cow milk [101,102] and neem leaf extract [103] are used to fabricate fluorescent GQDs by hydrothermal or microwave irradiation strategies. Low-cost organic compounds, such as citric acid [104][105][106][107][108][109][110][111][112], acetylacetone [113], glucose [114][115][116][117], fructose [118], ethylene diamine tetraacetic acid (EDTA) [119], adenosine 5′-triphosphate disodium salt (ATP) [119,120], glutamic acid [121] and humic acid [122], are also the most commonly used starting materials for the synthesis of GQDs either via pyrolysis or microwave irradiation or hydrothermal/solvothermal treatment. Moreover, due to their similarity in structure, polycyclic aromatic hydrocarbons are generally regarded as nanoscaled fragments of graphene, which gives them great promise for preparing monodispersed GQDs with precisely tailored structure, morphology and size.…”

“…Furthermore, doping and/or surface passivation are effective methods to modulate the electronic density of bulk semiconductor materials and to tune their optical and electrical properties. So, dicyandiamide (DCD) [105,106,112], ammonium hydroxide [77,89,91,93,114,115,[129][130][131][132], diethylenetriamine (DETA) [133], urea [107], ethylenediamine (EDA) [111], dimethylformamide (DMF) [38,134] and hydrazine hydrate [123] are chosen as the nitrogen source for doping or modifying GQDs to synthesize nitrogen-functionalized GQDs, while 1,4-phenylene bis(boronic acid) [65], boron oxide (B 2 O 3 ) [76] and Na 2 B 4 O 7 [135] are employed as boron sources to prepare boron-functionalized GQDs. Also, nitrogen and sulfur co-functionalized GQDs are successfully obtained using nitrogen and sulfur containing compounds of 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl) imide [68], polythiophene [136] and thiourea [110].…”