THERMOLUMINESCENCE EMISSION OF X-IRRADIATED EU2-CRYSTALS( DOPED KBR SINGLE)

In this paper we discuss the results of thermoluminescence (TL) studie s carried out on freshly quenched crystals of KBr doped with similar t o 50 ppm of Eu2+ ions which were X-irradiated at room temperature. The TL glow curve of this phosphor material consists of three glow peaks at 355, 376 and 398 K whose intensities increased as a function of X-i rradiation time. The TL glow peaks were analyzed by the total curve-fi tting method in order to obtain the characteristic parameters; activat ion energy, pre-exponential factor and kinetic order. The spectral cha racter of the emission recorded during thermoluminescence was found to be the same for all glow peaks and consists of a broad band centered at similar to 420 nm. This band is composed of two overlapping bands p eaking at 419 and 460 nm. The former band is due to the well known flu orescence of Eu2+ ions corresponding to the transition 4f(6)5d(T-2g) - -> S-8(7/2), while the latter may be associated with the recombination of F-centers with the radiation induced interstitial chlorine atoms w hich are thermally released from traps. It is proposed that the model of the TL Process most consistent with our experimental results is one in which the Eu2+ impurity acts as an electron trap during the irradi ation process and that the radiation induced center (partner of an F c enter) and the V-k center (partner of an Eu+ ion) are trapped together in the form of a Cl-3(-) molecular ion at the Eu2+-cation vacancy dip oles and their smaller aggregate complexes such as dimers, trimers, et c. During the TL run, the H and V-k centers escape from the trap and r ecombine with the complementary center giving rise to the observed TL emission spectra. The dosimetric characteristics of the KBr:Eu2+ phosp hor material are also reported.