Trapped Electron Centers and Trapped Hole Centers in Heavily Doped KCl: Tl. I. Thermal Glow Study

Abstract

Thermal glow curves of KCl crystals containing 0.2∼4.2 mole% of TlCl are measured after X-ray irradiation at 77 K. Trapped electron and trapped hole centers such as Tl 0 , Tl 2+ , Tl 2 + , (Tl 2 + )' and Tl 2 3+ centers are found to be concerned in the thermal glow phenomena. The features of the glow curves change remarkably with TlCl concentration because of marked reduction in the activation energies of the trapped electrons in a crystal containing more than 0.4 mole% of TlCl. This suggests that the bottom of the conduction band is disturbed by the influence of impurity potential. The emission spectrum of the glow also changes with TlCl concentration. A new emission band comes out around 500 nm and becomes dominant above 1 mole%. It is considered that trapped hole centers with complex structures take part in the electron-hole recombination process in such a heavily doped crystal.