Absorption Bands and Lines in Irradiated LiF

Abstract

The paper deals with a number of phenomena observed in lithium fluoride after formation of color centers by exposure to x‐rays, Van de Graaff electrons, or neutrons and not observed in other alkali halides under similar conditions. The most important of these phenomena are: (1) The appearance of a new band at 222 mμ, when the crystal is bleached with light of wavelength 254 mμ absorbed in the F band, and the inverse effect by subsequent irradiation with light of shorter wavelengths. (2) The production of F centers in a crystal heated to temperatures up to at least 450°C. The higher the temperature at which the F centers were produced, the greater is the intensity of the band at 222 mμ obtained by subsequent optical bleaching of the F band at room temperature. (3) The appearance of fine structure in a relatively weak band with peak at 380 mμ and of a very weak line at 523 mμ when the spectrum is recorded at the temperature of liquid nitrogen. (4) The very strong increase in the intensity of the band at 380 mμ and the line at 523 mμ by irradiation with short wavelength ultraviolet. (5) The sharpness at low temperatures of the first line of the band at 380 mμ and the line at 523mμ. At the temperature of liquid helium their half‐widths are of the order of 1A.