ELECTRONIC AND ATOMIC-STRUCTURE OF MN-DOPED CAF2 - AN X-RAY-ABSORPTION NEAR-EDGE STRUCTURE AND EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE STUDY

X-ray-absorption near-edge structure (XANES) and extended-x-ray-absorption fine-structure (EXAFS) measurements have been performed on the calcium K edge and manganese K edge of CaF2 doped with manganese at molecular concentrations of 0.1-2.5 %. The results are compared to other measurements of the calcium K edge in CaF2 and the Mn K edge in various manganese compounds. Major features in the XANES spectra are tentatively identified with transitions to high-symmetry points of the CaF2 energy bands in a one-electron picture. Expected deviations from the structure predicted by the one-electron formalism are discussed. The EXAFS analysis shows a reduction in the manganese-fluorine distance of (3.9+/-0.4)% as compared to the calcium-fluorine separation in the doped or undoped samples. This compares well with previous results obtained by EPR. A significant increase in disorder of the first shell around the Mn dopant ion is observed as compared to the Ca ion. The significance of this shell contraction and disorder is discussed in terms of possible defect structures in the material.