UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2002 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Optical properties of T-centers under gamma irradiation


Authors:
S.Polosan, E.Apostol, C.Dragusin*, V.Topa**


Affiliation:
INCDFM,76900, Bucharest-Magurele, Romania

*INCDFIN, 76900, Bucharest-Magurele, Romania

**Center of Advanced Studies in Physics, Bucharest Romania


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Keywords:


Abstract:
Electrolytic coloring of KCl crystals doped with Pb2+-ions (about 1017 ions/cm3), produce so called Ta centers in samples grown by high purity raw salt. Optical properties of these centers depend upon the codoping with alkali (Na+, Li+, Rb+- so called Tb and Tc centers) and Ca2+ ions (in the case of so called Td and Tx centers) . The most probably model of these T-centers is a Pb22- molecule situated in two adjacent negative vacancies, more or less perturbed. The aim of this paper is the attempting to destroy these centers by gamma irradiation and to obtain isolated Pb- centers. At room temperature, the irradiation process of crystal samples containing Ta, Tb, Tc, Td and Tx centers, change the optical properties of them, as follow: - the intensities of absorption bands in the u.v. range of Ta, Tb, Tc, Td centers are diminished by gamma irradiation - the emission spectra of Tb, Tc, Td and Tx exhibit clearly bands similar with AT and AX emissions of Pb2+-ions. The intensity of so called AX-band, in the case of Td centers, is higher than in other cases due to the concentration of Ca2+-ions which extend by two orders of magnitude the number of Pb2+-ions. - the illumination process are made in order to remove the F-centers, which appear with very high intensity after gamma irradiation, leads of increasing of Pb2+-ions emission. The explanations of these features are based on the fact that the production of Pb2+-ions by more easily detachment of electrons from Pb- and Pb0 centers comparing with Cl- ions. It cannot be excluded the possibility of existence of Pb+ and Pb0 centers in the samples.