Temperature dependence of the fundamental absorption tail of KCl and of the absorption due to bromine ions in KCl

Abstract

Optical absorption in the fundamental absorption tail of specially purified KCl and that due to bromine ions in KCl were measured between room temperature and 196°C. The latter was estimated from the difference between the fundamental absorption tails of pure KCl and KC1 with bromine of which the concentration was 1·3 × 10 −4 mole fraction. Measured absorption coefficients were corrected by considering the errors due to the finite band width of the spectrometer. The fundamental absorption tail of KCl was found to be represented by the Urbach rule with σ = 0·80 ± 0·02 and hv 0 = 7·76 ± 0·10 eV. The long wavelength side of the bromine absorption was describable by the same rule where σ = 0·51 ± 0·03 and hv o = 7·35 ± 0·15 eV.