  Photoluminescence (PL) features of nanostructured h-BN powder are studied in
the range of 200-600 nm in millisecond time window. It is found that four PL
excitation bands of 4.58, 5.01, 5.29, and 5.77 eV are characteristic of the
spectral region at hand. It is shown that the PL emission spectra can be
quantitatively described through a superposition of three Gaussian-shaped
peaks: 2.6, 3.1, and 3.7 eV. The observable luminescence is established to be
due to recombination processes involving centers whose energy levels in the
bandgap are formed by oxygen and carbon impurities, as well as nitrogen
vacancies and related complexes.
