Abstract
In the present work the impact of in situ photoreduction, by means of ultraviolet (UV) irradiation, on the nonlinear optical response (NLO) of some graphene oxide (GO), fluorographene (GF), hydrogenated fluorographene (GFH) and graphene (G) dispersions is studied. In situ UV photoreduction allowed for the extended modification of the degree of functionalization (i.e., oxidization, fluorination and hydrogenation), leading to the effective tuning of the corresponding sp2/sp3 hybridization ratios. The nonlinear optical properties of the studied samples prior to and after UV irradiation were determined by means of the Z-scan technique using visible (532 nm), 4 ns laser excitation, and were found to change significantly. More specifically, while GO’s nonlinear optical response increases with irradiation time, GF and GFH present a monotonic decrease. The graphene dispersions’ nonlinear optical response remains unaffected after prolonged UV irradiation for more than an hour. The present findings demonstrate that UV photoreduction can be an effective and simple strategy for tuning the nonlinear optical response of these graphene derivatives in a controllable way, resulting in derivatives with custom-made responses, thus more suitable for different photonic and optoelectronic applications.
Highlights
During the last decade graphene [1] has been among the most studied materials due to its extraordinary properties
The third-order nonlinear optical (NLO) response of G, graphene oxide (GO), GF and GFH has been investigated using the Z-scan technique [37], which allows the simultaneous determination of the sign and the magnitude of the nonlinear absorption and refraction of a sample from a single transmission measurement
The effects of the ultraviolet irradiation on the G, GO, GF and GFH dispersions were monitored through the collection and study of their respective UV–VIS–NIR absorption spectra after each irradiation cycle
Summary
During the last decade graphene [1] has been among the most studied materials due to its extraordinary properties. Various atoms and organic/inorganic molecules have been proposed and extensively used for the functionalization of graphene [18,19,20] Overall, these studies have confirmed that the modification of graphene’s surface with various atoms/molecules could alter the properties of graphene substantially, enabling the creation of a wide portfolio of newly synthesized graphene derivatives with tunable optical, chemical and mechanical properties. In the present work the 355 nm third harmonic output of a 4 ns Qswitched Nd:YAG laser was employed to irradiate some GO, GF and GFH dispersions for different irradiation periods and laser fluences, aiming to photo-induce significant changes in the sp2 /sp ratio of these graphene derivatives and modify their third-order nonlinear optical (NLO) response. Pristine graphene (G) dispersions were prepared and irradiated by the 355 nm UV laser light and their NLO responses were evaluated under the same experimental conditions used for the derivatives
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