Electrolytic reduction of Tl+ ions in KCl crystals

Electrolytic coloration has been made for KCl crystals doped with Tl+ ions and doped with Tl+ and Ca2+ ions. Intensity decrease of the Tl+ absorption bands is observed in the two colored crystals, while several new absorption and emission bands are observed. They are attributed to Tl− ions which were converted from Tl+ ions by electron injection during electrolytic coloration. Different absorption and emission bands are observed for KCl:Tl and KCl:Tl+Ca crystals. Sharp absorption band appears at 285nm in the colored KCl:Tl and at 400 and 503nm in the colored KCl:Tl+Ca. Infrared emission bands are observed at 1470, 1600 and 2185nm in colored KCl:Tl, while at 1630 and 1900nm in colored KCl:Tl+Ca. It is suggested that the absorption and emission bands in KCl:Tl+Ca are due to Tl− ions perturbed by Ca2+ or vacancy at the nearest neighbor.