Emission Spectra of KCl: Tl, KBr: Tl, and KI: Tl at 300, 80, and 12°K

Emission spectra have been measured for single crystals of KCl, KBr, and KI doped with about 0.01 mole% thallium. The measurements were made at 300, 80, and 12°K. Several new bands observed at 12°K are reported. An emission band which is centered directly on the $A$-absorption band is shown to be present in KI: Tl and KBr: Tl as well as KCl: Tl. An energy level scheme is suggested to explain the observed emission.