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Ohio State University

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Three types of electronic spectra, mostly from transition metals, have been observed in a variety of crystals. In the first type of spectrum the energy levels of the free ion are modified by the crystal field giving both sharp lines and broad bands which can be observed in absorption, or in some eases in fluorescence. The analysis of the spectrum can be carried out using the familiar crystal field theory. The spectrum of chromium as an impurity in several crystals, as well as that of cobalt in $CoF_{2}$ will be discussed. The second type of line spectrum arises from pairs of impurity ions coupled electronically in the lattice. The intensities of these lines relative to those due to the single ions vary with concentration, supporting the contention that they are due to pairs. A model for the orbital system involved will be presented to explain tile gross features of the pair spectra. The third type of spectrum is found in the ultraviolet region near the absorption edge of crystals doped with small concentrations of transition metals. The intensities of the broad bands observed suggest allowed transitions which may arise from one of at least two possible mechanisms. First an electron may transfer its association from the ligand anions to the central metal atom and produce a so-called charge transfer absorption. This may be recognized in crystals as an exertion process. Second there may be an internal allowed transition within the central metal ion from a 3d orbital to a 4p orbital. The structure of the spectrum produced by these two mechanisms is different, and the experimental results for Fe, Mn, Cr, Ti, V, and Co in $Al_{2}O_{3}$ will be discussed in the light of these differences.


Author Institution: Bell Telephone Laboratories Inc.