Optical excitations of boron nitride ribbons and nanotubes

The π-electronic structures of boron nitride ribbons and nanotubes are obtained from the tight-binding model. The absorption spectra are studied within the gradient approximation. They exhibit the prominent absorption peaks, mainly owing to the divergent density of states. The spectral intensity, the number of absorption peaks, and the excitation energies strongly depend on the geometry structures (ribbons or nanotubes, and zigzag structures or armchair structures). The characteristics of absorption spectra are associated with the selection rule and the state degeneracy. The 1D boron nitride systems, the zigzag ribbons excepted, have the same selection rule.