F Bands in Some Mixed Crystals of the Alkali Halides

X-ray induced F bands in melt-grown mixed crystals of KCl and RbCl were studied. Though no resolution of ``component'' F bands was obtained at liquid nitrogen temperature, the behavior of the F band parameters as a function of concentration of RbCl in KCl and as a function of temperature is shown to be explainable by postulating the existence of a set of ``component'' F bands, each arising from an F center with a given composition of positive ions immediately surrounding it. Some studies of other mixed crystals are also mentioned.