UCenter in Potasium Bromide

The absolute quantum efficiency for the destruction of $U$ centers and the formation of anion vacancies in KBr at 78°K has been found to be 0.61±0.07 when the $U$ optical absorption band is bleached by 225-mμ radiation absorbed at the maximum of the $U$ band. The quantum efficiency decreases significantly as the energy of the absorbed photons increases. It is suggested that the high-energy tail of the $U$ band is due to a secondary band and that the quantum efficiency of this band is 61 percent of that of the primary $U$ band. Previous results concerning the formation of isolated anion vacancies and interstitial hydride ions and interacting pairs of these entities are confirmed. However, the oscillator strengths of the perturbed $\alpha$ bands are found to be equal to that of the unperturbed $\alpha$ band.