Study of Tl+ion impurity in KI(Tl) by absorption spectroscopy and thermoluminescence

Single KI and that of Thallium-activated crystals have been grown by Czochralski Method in Argon atmosphere in home-made system at our laboratory. Then,the cleaved crystals annealed and exposed by γ-60CO irradiation .At all,the thermoluminescence and optical absorption of strained crystals have compared.These results, imply that the short wavelength absorption peaks of the phosphors which are not contained in the pure alkali halides are to be attributed to the excitation of the Thallium ions, such as Tl2+,Tl+ and Tl0.These centers are rather stable for optical bleaching. In conclusion,it seems to us that the main trapping levels are characteristic of the host lattice, regardless of the type of activator and the distortion in the crystal lattice in the neighborhood of the Thallium impurity provides the trapping sites for electrons,while the Tl+ ion acts as the luminescence center at which the emission takes place