Dual Fluorescence of Graphene Oxide: A Time-Resolved Study

Abstract

The fluorescence properties of graphene oxide (GO) was studied by recording the fluorescence lifetime, fluorescence emission, and excitation spectra, as well as UV-visible and near-IR absorption spectra. For the first time, we showed that a blue band (ca. 440 nm) and a long wavelength (LW) band (ca. 700 nm) are coexistent, which can be recorded simultaneously by controlling concentration, excitation wavelength, and pH values. Two bands are closely related by the protonation or deprotonation of GO. The blue band is favored by low GO concentration, short excitation wavelength, and high pH value, while the LW band is favored by low pH and long excitation wavelength. To reveal the nature of the dual emission of GO, the fluorescence lifetimes under various conditions were also measured. The blue band contains three emitting components; one of them has a lifetime as long as 10 ns, and its emitting intensity is fairly sensitive to pH, showing the potential for applications in sensing H(+) and fluorescence lifetime imaging. Combining the results under various conditions, we conclude that the electronic transition for this component is very likely due to n-π* transition. The LW band contains two main emitting components (0.2 and 2.1 ns) that also appear in the blue band as minor contributors; the related emission is assigned to π-π* transition. In summary, GO emission is of broadband (300-1250 nm), long-lived, pH sensitive, and excitation wavelength dependent. This makes it easily tailored for versatile applications.

Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

“…Unreduced GO produced a broad PL band at ~650 nm due to the π−π* transition, corresponding well with literature report 7,12 . As photoreduction progressed, PL was progressively redshifted and weakened.…”

“…Compared with GO, rGO has increased visible absorption, which has been attributed to restoration of the π network 7,9 or increased charge carrier concentration 10,11 . GO displays photoluminescence (PL) bands in the range of 500-800 nm, where PL in this range can originate from ensemble emission from sp 2 nanodomains of various sizes 7,12 . In contrast, thermally or photothermally reduced rGO shows fluorescence between 350 and 500 nm 13,14 .…”

The phosphorescence and excitation-wavelength dependent fluorescence kinetics of large-scale graphene oxide nanosheets

“…9,11,13,[16][17][18][19][20] This is in accordance with Wu's theory, where the ngerprint photoluminescence of the functional groups in GO was certied. Three PL peaks originate from the s*-n, p-p* and p*-n electronic transitions between the antibonding and bonding molecular orbitals.…”

“…To date, only a few groups have reported the PL spectroscopy of GO, which is found in the following wavelength ranges: the blue-centered (<450 nm), 7,[9][10][11][12] green-centered (450-490 nm)…”

On the Solvation Behavior of Graphene Oxide in Ethylene Glycol/Water Mixtures

“…The change in the GO concentration also affects pH of solutions, which in the studied concentration range varies from 4 to 6. However, as was demonstrated earlier,, such change in pH does not affect the UV/Vis spectra of GO solutions. Thus, an appearance of a second absorbing species at c >40 μg g −1 (hereinafter also called association point, c a ) is a result of the association processes occurring with increasing the GO concentration in water.…”