F Band Absorption in Alkali Halides as a Function of Temperature

Measurements have been made of the F centre optical absorption function for all twenty alkali halides at seven temperatures between ≈ 5 and 300 °K. The measurements have been fitted with a shape function consisting either of an unsymmetrical Gaussian band or, for the halides of cesium, of three symmetrical Gaussian bands of equal intensity, and the appropriate band parameters derived. The results are given of fitting the temperature variations of these parameters with the predictions of theory using one and two interacting vibrational modes. The variation of basic parameters from halide to halide is discussed.