Dipole Relaxation, Aggregation, and X-Ray Effects in KCl Doped with Eu++, Yb++, or Sm++

Abstract

The behavior of impurity-vacancy (I-V) dipoles has been studied in KCl single crystals doped with ${\mathrm{Eu}}^{++}$, ${\mathrm{Yb}}^{++}$, or ${\mathrm{Sm}}^{++}$, using the ionic-thermocurrents technique. The activation energies and frequency factors for dipole relaxation have been determined. The aggregation of these dipoles in KCl: ${\mathrm{Eu}}^{++}$ follows third-order kinetics in the temperature range 295-323 °K, and their decay rate is comparable to that of KCl: ${\mathrm{Sr}}^{++}$. The activation energy and frequency factor for the formation of trimers have also been determined. It has proved possible to destroy these rare-earth I-V dipolar systems by irradiation with x rays, and to recover them on subsequent heating or irradiation with a Xe-Hg lamp. This process is postulated to take place through charge conversion of the I-V dipole constituents.