Polarized Raman spectra of the oriented NaY(WO4)(2) and KY(WO4)(2) single crystals

Polarized Raman scattering spectra of the NaY(WO4)(2) (NYW) single crystal have been measured. Its structure is described in the tetragonal space grou p isomorphic to CaWO4 scheelite. The A(g), B-g, and E-g, spectra were made and discussed in terms of factor group analysis. These spectra are compared to those of monoclinic KY(WO4)(2) (KYW) single crystals whose structure di ffers from the other crystal. The NYW unit cell comprises of the isolated W O4 tetrahedra whereas the KYW structure is built from the WO6 octahedra joi ned by WO2W double bonds and WOW single bridges. The Vibrational characteri stics of the bridge bond systems are proposed. On this basis, the role of t he vibronic transitions for the KYW crystal doped with Eu3+ ions is discuss ed. (C) 2000 Elsevier Science B.V. All rights reserved.