Luminescence of Free and Relaxed Excitons in MgO

The vacuum ultraviolet luminescence of pure and doped MgO crystals excited by 10 keV electrons is studied in the temperature region 80 to 450 K. At 80 K the narrow edge luminescence band at 7.65 eV due to radiative decay of free excitons dominates in the emission spectrum of undoped crystals. At thermal quenching of this luminescence with an activation energy of (0.037 ± 0.005) eV, another luminescence band with maximum at 6.9 eV increases. The activation energy of this increase is (0.039 ± 0.005) eV. No relation of the 6.9 eV luminescence band with the presence of impurities and defects could be established and it is suggested to be due to radiative decay of relaxed (self‐trapped) excitons. [Russian Text Ignored].