“…In that case, powder samples were prepared by conventional solid-state synthesis. In our lab, we have succeeded in developing the same class of materials by the sol-gel process from metal alkoxides and lanthanide salts while the fluorination process occurs in situ by thermal decomposition of a fluorine-containing b-diketone during the firing treatment [11]. Starting from precursors at the molecular scale, this synthesis method is a convenient way to produce at low temperature high purity materials with chemical homogeneity.…”