Photoluminescence intensity time decay for the 2.8 eV blue emission band plotted on a logarithmic scale. The calculated time decay from the T-H model for acceptor Bohr radius of 5 Å is shown as indicated by the solid line. The fitting parameters are N=(5±1)x1019 cm-3, aA=5 Å and Wmax=(3±1)x107 sec-1.