Dramatic Enhancement of the Nonlinear Optical Response of Hydrogenated Fluorographene: The Effect of Midgap States

Abstract

The third-order nonlinear optical (NLO) response of hydrogenated fluorographene (CFH), a two-dimensional counterpart of graphane, was investigated in the visible and in the infrared, using nanosecond laser excitation, and compared to that of graphene fluoride (CF) and (unfunctionalized) graphene (G). All three graphenes were found to exhibit important NLO response, where CFH exhibiting the largest under visible and infrared excitations. In the visible, the response of CFH was determined to be two to three times larger than that of CF and G. However, in the case of infrared excitation, a dramatic enhancement that has not been previously observed for graphene derivatives was noticed, which is more than 2 orders of magnitude higher than that of CF and about 1 order of magnitude higher than that of G. This is attributed to the presence of midgap states which are formed upon functionalization of graphene and can enhance resonantly the NLO response of CFH. It is worth noting that the third-order nonlinear susceptibility χ(3) of hydrogenated fluorographene reached as high as 3 × 10–9 esu. To the best of our knowledge, this is a rather exceptional value for graphene derivatives.