Abstract
The optical absorption of single crystals of sodium chloride containing calcium as impurity has been measured. Results are given which show a new band at 345 mμ and from measurements of the bandwidth of the F-band it is deduced that the Z1-band is present in specimens, x-ray coloured, at room temperature.
The growth of the Z-bands on bleaching in samples containing differing amounts of calcium impurity and the effect of quenching was also studied. Rate equations are used to discuss the coloration of NaCl and are also applied to the complex (Ca2+. plus sign in box. 2plus sign in box minus sign in box) to explain the coloration of the crystals containing Ca2+.