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RESEARCH PRODUCT

About complexity of the 2.16-eV absorption band in MgO crystals irradiated with swift Xe ions

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Abstract The precise study of the accumulation and subsequent thermal annealing of the defects responsible for the complex absorption band around 2.16 eV, being under discussion in the literature for a long time, has been performed in highly pure MgO single crystals exposed to 0.23-GeV 132Xe ions with a fluence of Φ = 5 × 1011 − 3.3 × 1014 ions/cm2. Three Gaussian components with the maxima at 2.16, 2.02 and 2.40 eV have been considered as a measure of so-called D1, D2 and D3 defects. Similar to the F and F+ centers, the concentration of these defects increases at high fluences without saturation marks, thus confirming their radiation-induced nature (involvement of novel Frenkel defects). The accumulation of D1 and the first stage of D-type defect annealing up to 700 K occurs similarly to single F-type centers, while the following increasing stage for D2,3 starts above 700 K; their concentration reaches the maximum at 900 K (practically plateau is seen in this temperature region for D1) and complete annealing of the D-type defects proceeds at 1100 K. Behavior of the D1 defects (accumulation rate, annealing kinetic at high temperatures) clearly differs from that for other D-type defects (especially D2). In our opinion, the D1 defects are high-order aggregates of anion vacancies (and not the anion vacancy dimers), while the involvement of additional structural defects into the D2,3 defects is suggested.