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 °C different polycrystalline, almost single phase materials displaying μ-, α-, and β-cordierite crystalline forms were synthesized. In addition, spinel 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 μ-cordierite forms there are a large fraction of Co²⁺ in octahedral coordination, in the low (β-) and high (α-) 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 spinel, both displaying pure Co²⁺ tetrahedral coordination.