Local Site Symmetry Determination of Scheelite-Type Structures by Eu3+ Spectroscopy

SrWO4:x%Eu3+,Na+ (x = 0. 0.05, 0.5, and 5) have been prepared by the solid-state reaction method. Low temperature, high resolution emission and absorption spectroscopies have been employed to probe he local site symmetry of Eu3+ ions occupied the Sr2+ site in SrWO4 with a doping concentration up to 50 using Na+ as the charge compensation and, hence, to disapprove the formation of rnulticenters in the title compound containing trivalent lanthanide ions. The assignment of features in the 10 K visible emission spectra from D-5(0.1) -> F-7(J) (J = 0-4) multiplet terms and absorption spectrum from the ground-state level F-7(0) -> D-5(J) (J = 0-2) of SrWO4:Eu3+,Na+ is consistent with the predicted number of hands for certain transitions based on the point group selection rules for the S-4 site symmetry. The incorporation of Na+ together with Eu3+ into the SrWO4 lattice makes the vibronic bands associated with the D-5(0) -> F-7(J) (J = 0, 2, and 3) transitions shift to lower energy. The detailed spectroscopic interpretation conducted in this work serves as one of the few examples for Eu3+ accommodating the S-4 site symmetry, which have only been rarely performed previously in the host of LiYF4, and also gives insight into the assignment of lanthanide spectroscopy interpreted by forced electric and magnetic dipole selection rules.