Temperature Dependences of the Fundamental Absorption Tail of KCl and the Absorption due to Bromines in KCl

Optical absorptions of the fundamental absorption tail of specially purified KCl and those due to bromines in KCl were measured between room temperature and 196°C. The latters were estimated from the differences between the fundamental absorption tails of pure KCl and KCl with bromine of which concentration was 1.3×10 -4 in mole fractian. 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 h ν 0 =7.76±0.10 ev. The long wavelength side of the bromine absorption was able to be described by the same rule where σ=0.51±0.03 and h ν 0 =7.35±0.15 ev.