EPR Study of Impurity-Related Color Centers in Germanium-Doped Quartz

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Abstract
Since aluminum and germanium are two of the most easily incorporated impurities in crystalline quartz, the relationship of the color centers produced by x irradiation to these elements has been studied extensively. Previous work based on irradiation at 300°K has indicated that one type of electron‐deficient center is produced at aluminum, two kinds of electron‐excess centers are associated with germanium, and local charge neutrality is maintained by the insertion of an interstitial Na+ or Li+ ion at the germanium site. We have studied this system after irradiation at 77°K by conventional methods of EPR spectroscopy (9500 Mc/sec) and have discovered a new set of low‐temperature centers associated with these impurities. By identification of nuclear hfs and modification of the interstitial content through diffusion in an electric field, it is established that the same number of species is produced under these conditions but that the interstitial is located at the aluminum site. Detailed observations on the g tensors and hfs of the germanium centers are reported while observations on the aluminum centers are limited to the field orientation H ∥ c. By warming the crystals, efficient conversion of the low‐temperature centers to the high‐temperature forms is produced in crystals containing Na+ and Li+ for charge compensation. All low‐temperature forms are bleached completely by warming in samples in which the alkali ions have been replaced by H+, which is known to have a small mobility. While detailed models of all centers are not suggested, enough information was obtained to establish the relationship between the low‐ and high‐temperature forms. The experiments are correlated with optical results presented in an accompanying paper.

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