X-ray effects on cation impurity-vacancy pairs in KCl:Eu2+

X-ray irradiation of KCl: ${\mathrm{Eu}}^{2+}$ at room temperature destroyed impurity-vacancy ($I-V$) dipoles, converted the doubly valent impurity ion to a singly valent state, and created defect centers, e.g., $F$ centers and a 220-nm optical-absorption band. ${\mathrm{Eu}}^{+}$ produced by the irradiation was observed to grow in proportion to the destruction of ${\mathrm{Eu}}^{2+}$. The 220-mμ band was also observed to grow approximately in proportion to the height of the $F$ band, in agreement with previous workers. The number of dipoles destroyed was equal to or exceeded the sum of the number of converted ions and the number of $F$ centers produced. A possible explanation of these results is that x rays increase the rate of aggregation of dipoles. It is likely that it is the cation vacancies bound in $I-V$ dipoles that are converted to anion vacancies which later form $F$ centers.