  Photoluminescence of polycrystalline hexagonal boron nitride (hBN) was
measured by means of time- and energy-resolved spectroscopy methods. The
observed bands are related to DAP transitions, impurities and structural
defects. The excitation of samples by high-energy photons above 5.4 eV enables
a phenomenon of photostimulated luminescence (PSL), which is due to distantly
trapped CB electrons and VB holes. These trapped charges are metastable and
their reexcitation with low-energy photons results in anti-Stockes
photoluminescence. The comparison of photoluminescence excitation spectra and
PSL excitation spectra allows band analysis that supports the hypothesis of
Frenkel-like exciton in hBN with a large binding energy.
