For characterization of luminescence duration we had
approximated decay with exponent. In such case the fast time
constant of decay is about 37 ns at 9 K (Fig. 6 open squares). Fig. 6
shows that decays, within the fast and slow PL bands are practically
uniform, from 2 eV to 3.2 eV but change dramatically above
3.3 eV, where the PL intensity peaks at 4.4 and 5 eV for the slow
and fast components respectively. This shift is of about 0.6 eV is
likely due to singlet–triplet splitting of excited states of a single
center. Temperature dependences of time-resolved intensities and
time constants are very similar in crystal, Fig. 7 for fast component
of decay approximate in the range of tens of ns. In the ms range,
shown in inset Fig. 7,