EPR investigations on X-ray and photo-induced processes in ZnO coating material

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.