Spectroscopic properties of Co2+ in related spinels

We report the absorption and fluorescence spectra of divalent cobalt (Co2+) in a series of related spinels Mg(1−x)CoxAlBOC, where B=2, 4, 6, C=4, 7, 10, and x represents the amount of Co2+ that substitutes for Mg2+ in tetrahedral sites of Td symmetry. The spectra support the assumption that both Mg2+ and Co2+ prefer the tetrahedral cation sites during the growth of these crystalline materials. These observations also support earlier conclusions obtained from crystallographic and thermodynamic studies of the MgO and Al2O3 phase diagram. The observed spectra are analyzed and compared to calculated electronic levels derived from lattice-sum models using crystallographic data determined from the crystals grown in the present studies. Comments are made in relevance to the use of these crystals as saturable absorbers for near infrared Q-switched lasers.

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