Excitation and High-Temperature Absorption of KCl: Tl

Optical measurements have been made on crystals of KCl with a wide range of thallium concentrations. Absorption measurements have been made up to 560°C and excitation spectra for luminescence have been measured from liquid nitrogen temperature to 100°C. These measurements, in conjunction with earlier work, lead to the conclusion that there are at least seven bands in KCl: Tl: three in the "$A$" band region and two each in the "$B$" and "$C$" band regions. The large shift from "$C$" band to "$B$" band at high temperatures which has been previously reported was not found here. It is noted that the addition of small amounts of Sr to KCl shifts the fundamental absorption edge to short wavelengths.