Sol-Gel-Synthesis of Nanoscopic Complex Metal Fluorides

The fluorolytic sol-gel synthesis for binary metal fluorides (AlF(3), CaF(2), MgF(2)) has been extended to ternary and quaternary alkaline earth metal fluorides (CaAlF(5), Ca(2)AlF(7), LiMgAlF(6)). The formation and crystallization of nanoscopic ternary CaAlF(5) and Ca(2)AlF(7) sols in ethanol were studied by (19)F liquid and solid state NMR (nuclear magnetic resonance) spectroscopy, as well as transmission electron microscopy (TEM). The crystalline phases of the annealed CaAlF(5), Ca(2)AlF(7), and LiMgAlF(6) xerogels between 500 and 700 °C could be determined by X-ray powder diffraction (XRD) and (19)F solid state NMR spectroscopy. The thermal behavior of un-annealed nanoscopic ternary and quaternary metal fluoride xerogels was ascertained by thermal analysis (TG/DTA). The obtained crystalline phases of CaAlF(5) and Ca(2)AlF(7) derived from non-aqueous sol-gel process were compared to crystalline phases from the literature. The corresponding nanoscopic complex metal fluoride could provide a new approach in ceramic and luminescence applications.