Third-order nonlinear optical properties of carboxyl group dominant carbon nanodots

We quantitatively investigate the nonlinear optical (NLO) property of carbon nanodots (CNDs, less than 10 nm) by the Z-scan technique using a tunable 532 nm nanosecond laser system. These CNDs were fabricated by an electrochemical etching method from graphite rods. Our results suggested that the third-order nonlinear susceptibility chi((3)) of CNDs is strongly dependent on the diameter of the CNDs apparently; the nonlinear refractive index gamma decreased as the size of CNDs decreased, while the nonlinear absorption coefficient beta showed an opposite tendency to gamma. We further demonstrated that the carboxyl group on the CND surface plays a key role and has significant impact on the third-order nonlinear susceptibility chi((3)).