Electron Traps in the Thallium-Activated Potassium Chloride Phosphor

The effects of activator concentration, added impurities, infrared stimulation, and temperature of excitation on the thermoluminescence of KCl:Tl permit the identification of the two principal trapping levels as the 3P00 and 3P20 states of isolated Tl+. The energy of activation necessary to fill these metastable states, following excitation to the 3P10 and 1P10 states, is provided by the polarization energy. The concentration of traps simultaneously filled is limited primarily by re-excitation of metastable Tl+. F and V centers are created by multiple excitation of Tl+. These interpretations are quantitatively correlated by a configuration coordinate model and are shown to be in accord with the band theory.