Evolution of the structural and optical properties from cobalt cordierite glass to glass-ceramic based on spinel crystalline phase materials

CO2+-containing cordierite stoichiometric glasses have been prepared by melting colloidal gel precursors. After controlled thermal processing in the range of temperatures between 900 and 1300 degrees C different polycrystalline, almost single phase materials displaying mu-, alpha-, and P-cordierite crystalline forms were synthesized. In addition, spinet glass-ceramic materials were also prepared from the base glasses. All these materials were characterized by X-ray powder diffraction and infrared spectroscopy. Room temperature (RT) absorption and emission spectra of Co2+-cordierites and - spinel-glass material have allowed determining the local environment of the Co2+ in the crystalline structure of final materials. Results indicated that whereas in parent glasses and in the t-cordierite forms there are a large fraction of CO2+ in octahedral coordination, in the low (beta-) and high (alpha-) temperature crystalline forms the proportion of Co2+ in tetrahedral coordination increased. The final CoAl2O4-glass composite showed absorption and emission spectra very similar to the sol-gel CoAl2O4 spinet, both displaying pure Co2+ tetrahedral coordination. (c) 2007 Elsevier B.V. All rights reserved.