“…For a long time, MgO single crystals doped with different impurity ions (Be 2+ , Ca 2+ , Zn 2+ , Al 3+ , Li + , Na + , F − , OH − , etc) have been grown for various purposes at the Institute of Physics, Tartu. These crystals have been investigated using different methods including the EPR and measurements of cathodoluminescence spectra through double monochromators in a wide region of 1.6–11 eV at 6–420 K. A doping of MgO with impurity ions, isovalent to cations Be 2+ and Ca 2+ , leads to the appearance of short‐wavelength broad luminescence bands with the maxima at hν > 0.5 E g (such inequality is typical of a mobile electron in the related e–h recombination process) that definitely correspond to the recombination of the electrons relaxed down to the bottom of the conduction band with the holes localized near impurity cations 30, 35. Ca 2+ and Be 2+ ions serve as hole traps forming Coulomb [hCa] + and [hBe] + trapped‐hole centers with large cross‐sections (at least by two orders of magnitude larger than that for the neutral traps) for the recombination not only with the electrons relaxed to the bottom of the conduction band, but with non‐relaxed (hot) e as well.…”