Experimental Study of the Shape of the F-Band Absorption in KCl

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Abstract
The optical absorption due to F centers in KCl at temperatures between 4°K and 377°K has been measured. The authors believe they have eliminated the K band, and obtained the absorption due to transitions from the ground to the first excited state. The method of preparing ``pure'' F centers is discussed. The halfwidth, the point of maximum absorption, and the zeroth, first, and second moments have been measured in the above temperature range. The data establish Smakula's formula on a firm experimental basis for this center. The half-width in ev is given by the relation 0.163 [coth(71.0/θ)]12, while the point of maximum absorption is at 2.340–0.027 coth(71.0/θ), where θ is the absolute temperature. An equation has been found from which one may calculate the F band absorption. The shape of the band is temperature independent and is approximated by the low temperature form predicted by Pekar. The data on the whole support a generalized theory. The authors believe that the F band shape is due to the interaction of the F electron with localized modes whose average ground state frequency is 2.96×1012 sec—1.

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