Localization of Eu3+ in KGd1.9Eu0.1F7 and KGd1.9Eu0.1F6.97O0.015 by site-selective excitation and time-resolved spectroscopy

This paper reports site-selective excitation (or observation) and time-reso lved spectroscopy of the host matrices KGd2F7 and KGd2F6.97O0.015 doped by Eu3+. The crystal structure of KGd2F7 derives from that of the fluorite-typ e, by an ordering of the cations and anions. The luminescence spectra and s ite-selective excitation in the D-5(0)-->F-7(0) region, have allowed to ide ntify several distributions of discrete sires for the Eu3+ ions, in which t wo sites are characterized by unusual spectra which are attributed to Eu-O bonds. Another kind of site, characteristic of fluorinated surroundings clo se to the centrosymmetry, exhibits a very long lifetime (6.8 ms) of the D-5 (0) level. Although the accurate structures of these compounds are not yet known, they are very close to that of KGd2.77F9.32 previously solved and th e spectroscopic results are in agreement with the number and the symmetries of the rare earth crystallographic sites. (C) 1999 Elsevier Science S.A. A ll rights reserved.