Nonlinear optical properties of carbon nitride nanotubes

Abstract

The second order polarizabilities (β) of the C₃N₄ NT systems were investigated in this study. The β values of end groups substituted C₃N₄ NTs were calculated to find their most favorable paradigm for nonlinear optical design. It was found that their electric dipole transitions are only allowed along the tube axis direction and the position of terminal groups has a great effect on NLO properties of substituted C₃N₄ NTs. The obtained results provide us details to understand the relation between the structure and nonlinear optical properties. The results indicate that the second-order polarizabilities originate from charge transfer from a donor (–NH₂) to an acceptor (–O₂N) and the electron density redistribution in heptazine units. We employ a one-dimensional two-state model to analyze the nature of the second-order polarizabilities of studied materials. The frequency-dependent second-order polarizabilities were also calculated. The second-order polarizability of the O₂N–C₃N₄–NH₂ NT is 2.51 × 10⁻²⁷ esu when the input photon energy is 2.232 eV, which is much larger (about two orders of magnitude) than static second-order polarizability (2.54 × 10⁻²⁹).