O−−-Lücken-Dipole in Alkalihalogenidkristallen

Dielectric loss measurements are reported for KBr, KCl, and NaCl crystals containing O^?? ions. The frequency and temperature dependences can be well represented by a Debye curve. The dipole moment found immediately after quenching is interpreted as being due to O^?? ions associated with anion vacancies. Activation energies for reorientation of the ion are E₀=0.59 eV for KCl, 0.54 eV for KBr and 0.61 eV for NaCl. Fluorescence bands were found in freshly quenched KCl crystals at 470 nm and 1.05 μm and are attributed to isolated dipoles. Dielectric losses decreased and the optical absorption changed during annealing due to the collection of centers into aggregates. A detailed analysis of the kinetics for KCl indicates the formation of double dipoles as the first step. The energy of association is E_A=0.85 eV. Earlier measurements of absorption, fluorescence and photochemical coloring are reinterpreted on the basis of the proposed model in which an O^?? center is thought of as a O^?? ion associated with an anion vacancy.