Single crystals of MgO have been additively colored by heating them in Mg vapor at temperatures from 1600 to 1800'C and pressures up to 4000 Torr. The F+ and F' optical absorption bands (due to anion vacancies containing one and two electrons, respectively) were observed to be extremely similar but distinguishable, and were observed at liquid-nitrogen temperature to peak at 4.96 and 5.03 eV, respectively.The oscillator strength for the F' center is estimated to be 0.70&0.05. A photoconversion process F+~F' was studied. The luminescence bands for these centers were observed at 3.1 and 2.4 eV, respectively. The density of F' centers 1' produced by the additive coloring process was observed to be related to the density of atoms in the vapor $«by the equation EF =1270K«e @'~~, where Q=1.53 eV. The temperature dependence of these two bands was measured and is discussed.

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The use of zinc oxide (ZnO) powder as a thermal control coating material for spacecraft has been investigated by electron paramagnetic resonance (EPR) technique. The EPR signal of the photosensitive donor at g = 1.9557 is shown to be influenced by X‐rays, temperature, and light irradiation. The activation energy (trap depth) is deduced from isothermal decay experiments applying the cross‐cut method. The estimated value of E = 0.52 eV corresponds to optical data. After X‐ray irradiation at 88 K, the EPR signal is no longer photosensitive; increasing temperature causes an annealing of this X‐ray‐induced effect. The annealing process is correlated with the thermoluminescence glow curve. The excitation spectra and photoquenching of the EPR signal have been measured. Radiation damage after high dose irradiation is investigated with regard to the degradation process.

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