Thermal Bleaching ofVBands at Room Temperature in Alkali Iodide Crystals Containing Excess Iodine

Abstract

Thermal stability of V centers has been investigated at room temperature (RT) for additively colored alkali-iodide crystals by means of optical absorption measurements. V 2 and V 3 bands due to V centers in the crystal were gradually bleached by annealing at temperatures near RT. The bleaching rate of the bands is proportional to the square of the V -center concentration. The activation energies for bleaching of the V bands in KI and RbI crystals are estimated from the bleaching rates to be 0.85±0.04 eV and 0.82±0.03 eV, respectively. The V 2 bands in the crystals containing divalent cations bleach only weakly at RT. The effect of impurities, such as divalent cations, on the thermal stability of the V centers will be discussed.