Luminescence decay and electron traps in thermochemically reduced MgO.

We report an analysis of the decay curves for 2.3-eV F-center luminescence in several samples of thermochemically reduced MgO. Previous measurements have shown that the concentration of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions in a sample determines the lifetime of the luminescence at 260 K. We show here that the decay tends to become approximately second order in a characteristic time \ensuremath{\tau}, which depends on the concentrations of traps in the crystal, especially ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ ions. At room temperature \ensuremath{\tau} is smallest for the sample containing the largest relative ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$-ion concentration, whereas at 40 K the converse is found to be the case. These results are explained semiquantitatively in terms of a general theoretical model involving two kinds of electron traps with different thermal activation energies.