PREPARATION AND CHARACTERIZATION OF ALKALI AND ALKALINE EARTH-BASED RARE-EARTH SULFIDES

Various alkali- and alkaline earth-based cerium and neodymium sulfides (A, Ln)(3)S-4 (A = Li, Na, Ca, Sr) have been prepared by solid state routes. XRD and Ln L-III-edge EXAFS studies showed that the first and second coordination shells corresponding to the two LnS(4) tetrahedra remain quasi-identical whatever the A cations, while the further coord ination shells around 4 Angstrom change drastically due to the presenc e of A cations. Such a cationic distribution may influence the chromat ic properties of these compounds. Furthermore, fluorination treatment of Na0.5Ce2.5S4 sulfide leads to an improvement of the reflectance at lambda > 640 nm attributed to the presence of CeF3 at the grains surfa ce and to a modification of the microstructure of this material. (C) 1 998 Published by Elsevier Science B.V.