N-Doped carbon dot with surface dominant non-linear optical properties
We quantitatively investigated the nonlinear optical (NLO) property of N-doped carbon dots (N-CDs, obtained from C3N4) by the Z-scan technique with a tunable 532 nm laser system. The third-order nonlinear susceptibility χ(3) of N-CDs (0.63 g L−1) measured under nanosecond and picosecond laser were 12.5 × 10−12 and 0.725 × 10−12 esu, respectively. In the case of ns laser irradiation, the χ(3) were about one order of magnitude higher than that of boron doped CDs, while about two orders of magnitude higher than that of boron doped CDs under ps laser excitation compared with the results that reported by Bourlinos et al. We also point out that the differences in susceptibility may be result from the differences in order of nitrogen and nitrogen doping content. We further demonstrated that the carbonyl group on the surface of N-CDs plays a key role and has significant impact on their third order susceptibility χ(3). A rough theoretical analysis was also carried out for the explanation on the NLO property of the N-CDs.