QUALITATIVE AND QUANTITATIVE STUDIES OF NEODYMIUM DOPED SILICA GEL-GLASSES

Abstract

The effect of neodymium ions on establishment of the sol-gel matrix and of the sol-gel matrix on the metal ion chemistry has been investigated by spectroscopic techniques including FTIR, FTNIR and UV/Vis. Materials were prepared by the pre-doping method and contained metal ions added as the chloride in either the aqueous or alcoholic phase at initial solution concentrations between 10−7 M and 1 M. The presence of the metal ions affects the rate of drying of the gel-silicas and can reduce the time required for weight stabilization by ca. 50%. Irrespective of the solvent system used for metal ion incorporation, the metal ions are found in 9-fold coordination sites in the as-prepared gels, in 8-fold coordination sites in gels where solvent has been removed by evacuation and for gels heated to 800°C, a highly symmetric environment (concentrations of 0.01 M and below) or 8-fold solid-state coordination where there is a degree of covalent character between the liganding atoms and the metal ions. Metal ion concentration and absorbance are related for gel-silicas prepared with dopants at initial concentrations of 0.01–1 M, although the absorbances measured depend on the solvent used for incorporation of the metal ion. Experimental data suggest that the matrix and metal ions interact at various stages in the formation of the doped gel-silica, however, we do not presently know if these interactions are transitory or permanent in nature.