Kinetics of radiative recombination in magnesium oxide

We report time-resolved studies of luminescence excited in nominally pure single-crystal MgO by short pulses of 500-keV electrons at sample temperatures from 10 to 500 K. The principal luminescence bands have peaks at approximately 4.9, 3.3, and 1.7 eV. The decay kinetics and spectral shift of the 4.9-eV luminescence band can be accounted for by the theory of tunneling recombination between randomly distributed hole and electron traps. From prior work, the hole trap has been identified as a magnesium ion vacancy. The electron trap has not been identified, but there is some evidence to suggest that a substitutional O${\mathrm{H}}^{2\ensuremath{-}}$ molecular ion could be the neutral donor. The temperature dependence of the luminescence decay has been modeled by including thermal ionization of one trap as a de-excitation channel in parallel with tunneling recombination. Depending on conditions, this thermally-induced hopping of charges can enhance or quench the luminescence.