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 50ppm of EU(2+) ions which were X-irradiated at room temperature. Th e TL glow curve of this phosphor material consists of three glow peaks at 355, 376 and 398K 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 EU(2+) ions corresponding to the transition 4f(6)5d (T-2g ) --> S-8(7/2), while the latter may be associated with the recombinat ion of F-centers with the radiation induced interstitial chlorine atom s which are thermally released from traps. It is proposed that the mod el of the TL process most consistent with our experimental results is one in which the EU(2+) impurity acts as an electron trap during the i rradiation process and that the radiation induced center (partner of a n F center) and the V-k center (partner of an Eu+ ion) are trapped tog ether in the form of a Cl-3(-) molecular ion at the Eu2+-cation vacanc y dipoles and their smaller aggregate complexes such as dimers, trimer s, etc. During the TL run, the H and V-k centers escape from the trap and recombine with the complementary center giving rise to the observe d TL emission spectra. The dosimetric characteristics of the KBr:Eu2phosphor material are also reported.