Two-dimensional two-photon absorptions and third-order nonlinear optical properties of i _hfullerenes and fullerene onions

The third order static and dynamic nonlinear optical (NLO) responses of Ih symmetry fullerenes (C60, C240, and C540) and fullerene onions (C60@C240 and C60@C240@C540) are predicted using the ZINDO method and the sum-over-states model. The static second hyperpolarizability of Ih symmetry fullerenes increases exponentially with fullerene size [from 10.00 × 10-34 esu in C60 to 3266.74 × 10-34 esu ≈ γ0(C60) × 92.63 in C540]. The external fields of strong third order NLO responses of Ih symmetry fullerenes change from ultra-violet (C60) to the visible region (C540) as the fullerene size increases. The outer layer fullerene in the fullerene onions has dominant contributions to the third order NLO properties of the fullerene onions, and the inter-shell charge-transfer excitations have conspicuous contributions to the third order NLO properties. The two-dimensional two-photon absorption spectra of C60 and C240 show that those fullerenes have strong two-photon absorptions in the visible region with short wavelength and in the ultra-violet region.