Raman Spectroscopy and Time-Resolved Photoluminescence of BN and B<i>_x</i>C<i>_y</i>N<i>_z</i> Nanotubes

We report Raman and time-resolved photoluminescence spectroscopic studies of multiwalled BN and BxCyNz nanotubes. The Raman spectroscopy shows that the as-grown BxCyNz nanotubes are radially phase separated into BN shells and carbon shells. The photoluminescence decay process is characterized by two time constants that are attributed to intra- and inter-BN sheet charge recombination, respectively. A comparison of the photoluminescence of BN nanotubes to that of hexagonal BN is consistent with the existence of a spatially indirect band gap in multiwalled BN nanotubes as predicted by theory.