OPTICAL AND ELECTRICAL STUDIES OF COLLOIDAL AND F-AGGREGATE CENTERS IN HIGHLY PURE KBR CRYSTALS

The optical and thermal stability of F, M, R bands and colloids in KBr is measured. Extensive measurements on conductivity of the additively colored crystals are reported. Excess electronic conductivity is observed; it is due to M centers below 150 °C and to colloids between 300 and 450 °C. The background divalent cation impurities suppress the excess conductivity due to M centers and colloids, and reduce the ionic conductivity at ∼300 °C to a value much less than that of a similar uncolored crystal. The influence of light on the excess and the ionic conductivity in the colored KBr crystals is also discussed. OH- impurity enhances both the optical colloidal band and the excess conductivity associated with it. The results are compared with those obtained by us recently for KCl crystals. © 1969 The American Physical Society.