Color Centers in X-Rayed Potassium Iodide

Single crystals of potassium iodide have been irradiated with x-rays at room, liquid nitrogen, and liquid helium temperatures. Only a negligible $F$-center production occurs at liquid helium temperatures, whereas a greatly increased rate prevails at normal temperatures. A number of new absorption bands have been found to occur at liquid helium temperature, whereas the room and liquid nitrogen temperature spectra are much simpler. At least two of these bands are shown to be associated with impurities. Spectra are presented which show the initial existence of centers with absorption bands near the fundamental absorption edge in the unirradiated crystal. Evidence is presented which shows that the initial effect of irradiation is to lower the absorption in the long-wavelength tail of the fundamental absorption band, presumably by radiation damage of those nonequilibrium aggregates initially present in the crystal. More certain purity is required for further studies.