Color Centers and Trapped Charge in KCl and KBr

Potassium chloride and bromide crystals have been irradiated with x-rays at -183°C and the behavior of the $V_1$, $F$, and $F^{\prime }$ optical absorption bands observed during subsequent warming to room temperature. The thermal bleaching of the $V_1$-band is accompanied by a decrease in the $F$-band, the appearance of free charge within the crystal, and luminescence. The data indicate that positive holes are released from traps during this process.