OPTICAL-SPECTRA OF OXYGEN DEFECTS IN BAFCL AND BAFBR CRYSTALS

Oxygen impurities enter BaFCl and BaFBr crystals as oxygen-vacancy centers. As in other ionic crystals, these defects in the barium fluorohalide crystals have several absorption bands and one photoluminescence band. The defects also are involved in aggregation and photochemical reactions. We have found two kinds of oxygen-vacancy centers in barium fluorohalide crystals and denoted them as centers of types I and II. On the basis of the growth conditions, absorption spectra and other data one may conclude that centers of the first type consist of oxygen substituting at F- sites and neighboring Cl or Br- vacancies. Oxygen-vacancy centers of the second type seem to be completely on either the Cl or the Br sublattice.