Abstract
An attempt has been made to interpret natural sapphire optical absorption spectra with regard to the exchange-coupled pairs of iron impurities in their ferric and ferrous states. Level schemes have been calculated for Fe3+-Fe3+ and Fe2+-Fe2+ pairs of all the orders, their symmetry being observed. The selection rules are discussed. EPR and infrared spectroscopy information has been used to assist the optical spectroscopy data. The sapphire color has been interpreted as a function of Fe2+/Fe3+ ratios and of the presence of their pairs in the stone. The various types of charge compensation in Fe2+→Al3+ isomorphism are discussed.
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Nikolskaya, L.V., Terekhova, V.M. & Samoilovich, M.I. On the origin of natural sapphire color. Phys Chem Minerals 3, 213–224 (1978). https://doi.org/10.1007/BF00633571
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DOI: https://doi.org/10.1007/BF00633571