Crystal-field analysis of Eu3+ energy levels in the new rare-earth R BiY1-xRxGeO5 oxide

Pale colored BiY1-xRxGeO5 (R = rare-earth from Pr to Yb) polycrystalline samples exhibit a crystalline phase isostructural with the orthorhombic Pbca (No. 61) structure-type established for BiYGeO5 and BiYbGeO5. R occupies a single point site in the host, with the lowest C-1 symmetry. While for Pr and Nd x must be less than or equal to0.35, for smaller R ions, Sm to Yb, the phase appears for any x content. Detailed crystallographic data for BiErGeO5 have been determined from the structure refinement of its neutron diffraction profile at room temperature. Optical absorption and photoluminescence measurements at 10 K have been performed for BiEuGeO5 An initial approach to the parametrization of crystal-field effects on this new host has been provided by results of the semi-empirical Simple Overlap Model, which considers the crystallographic positions of the nearest neighbors around R. Furthermore, the strongly reduced F-7(JM) set of levels of the 4f(6) configuration has been taken into account for a trustworthy phenomenological determination of crystal-field parameters of the observed optical center for the Eu3+ sample. In spite of difficulties imposed by the low symmetry of Eu3+, a very good root mean squares deviation sigma = 5.6 cm(-1) between experimental and simulated energy level schemes has been obtained considering the approximate C-2(C-s) symmetry for the Eu3+ in the host. (C) 2003 Elsevier Science (USA). All rights reserved.