Optical spectra of single-walled boron nitride nanotubes

The optical properties of different single-walled boron nitride nanotubes (SWBNNTs) with respect to their chirality, tube length, and tube diameter are examined with a time-dependent localized-density-matrix approach based on a semiempirical Hamiltonian. Comparisons to single-walled carbon nanotubes (SWCNTs) are made where appropriate. It is found that the optical gap of SWBNNTs is independent of the chirality with a given tube diameter. The gap is 5.78 eV at a tube diameter of about 5.6 Å, in contrast to SWCNTs, in which the optical gap depends strongly on the chirality, especially when the tube diameter is small. It is also found that SWBNNTs mainly show one major absorption peak below 6 eV, which is very different from the multipeak features of SWCNTs. Moreover, the optical properties of SWBNNTs are also found to be strongly anisotropic and significantly high in absorption intensity regardless of the chirality, suggesting a good potential in advanced applications such as ultraviolet light absorption.