LUMINESCENCE OF LEAD IONS ASSOCIATED WITH INTERSTITIALS AND VACANCIES IN ALKALI-HALIDES

Several types of luminescent associates of lead ions (Pb2+,Pb+) with interstitial halide ions (X(i-)) as well as with cation (v(c)- and anion (v(a)+ vacancies are observed in alkali halides X-irradiated at 80 or 295 K. Optical properties and a detailed structure of these associates, the processes of their creation and destruction as well as their optically or thermally stimulated transformations are studied. The associates investigated form the three following groups each containing several types of centres: 1) centres on the basis of a PbX2- -molecular ion; 2) centres on the basis of a Pb2+X(i)- dipole; and 3) centres of the laser-active structure on the basis of a Pb+X-v(a)+ associate. The optical characteristics of the various centres of each group are shown to be similar. It is concluded that they are determined by electronic transitions between the energy states of the basis associate (PbX2-, Pb2+X(i)-, or Pb+X-v(a)+), and that the influence of some other defects (v(c)-,X(i)-,X3-, etc.) may be considered as a small perturbation.