XAS study of chromium in Li2MSiO4 (M=Mg, Zn)

X-ray absorption spectroscopy (XAS) investigations at the Cr K-edge on Cr:Li2MSiO4 (M = Mg, Zn) have been performed to understand the exceptionally long fluorescence lifetime of Cr-IV. Previous work has shown the simultaneous presence of three oxidation states Cr-IV, Cr-V and Cr-VI. X-ray absorption near edge structure measurements confirm that Cr in Li2MSiO4 (M = Mg, Zn) single crystals is in tetrahedral coordination. They also reveal that Cr-VI is the dominant species in Li2MgSiO4, and that Li2ZnSiO4 contains more Cr-V than Li2MgSiO4. The extended X-ray absorption fine structure spectra of Cr:Li2MgSiO4 single crystals recorded at the Cr K-edge, are fitted with two types of Cr environments: the first one corresponds to oxygen atoms at a mean distance of 1.68 Angstrom and the second to oxygen atoms at a mean distance of 2.07 Angstrom. This second environment is attributed to Cr-III. in the minor parasitic phase (LiCrO2)-O-III. The first environment corresponds to Cr that substitutes silicon in the Li2MgSiO4 lattice in the silicon site if the cations sizes are considered. (C) 2002 Elsevier Science B.V. All rights reserved.