The U center in potassium bromide crystals

The optical bleaching of the U band in potassium bromide crystals at 78°K has been investigated. The nature of the secondary bands, the U' and the Ul bands, was studied. The U' band consisted of component bands, including the a band which is due to exciton transitions near a negative ion vacancy. One component of the U' band is bleached readily in either of two ways: either by warming the crystal to lo6°K or by irradiating with monochromatic light in the Ul band. This component of the ut band was interpreted as due to exciton transitions near a negative ion vacancy perturbed by the proximity of a Ul center, that is, an interstitial hydride ion. The spectral distribution of quantum efficiency for conversion of U centers to negative ion vacancies at 78°K was measured and found to decrease by 4~ on the high energy side of the U band. The U band has a high energy shoulder and it is suggested that this high energy shoulder exhibits a lower quantum efficiency for the conversion than does the main U band.U of I OnlyThesi