INFRARED LUMINESCENCE AND ABSORPTION SPECTRA FROM EXCITED STATES OF THE F CENTER IN CaO
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Date
1974
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Ohio State University
Abstract
The F center in calcium oxide consists of two electrons trapped at a vacant $O^{2-}$ site. Calculations indicate that the ordering of the electronic energy levels from the ground state is $^{1}A_{1g}$, $^{3}T_{1u}$, $^{3}A_{1g}$, $^{1}T_{1u}$. The $^{1}T_{1u}$ level presumably lies just below the conduction band. An absorption band due to the $^{1}A_{1g}$ $\rightarrow$ $^{1}T_{1u}$ transition is observed at 400 nm at $300^{\circ} K$, and a characteristic long-lived orange emission band at 601 nm is apparently due to the $^{3}T_{1u}$ $\rightarrow$ $^{1}A_{1g}$ transition. Investigations of the level scheme of this center have been made by laser-excited infrared and visible luminescence and by pseudo-two photon absorption techniques. A luminescence band centered at approximately 600 $cm^{-1}$ at $80^{\circ} K$ is tentatively assigned to the $^{3}A_{1g}$$\rightarrow$ $^{3}T_{1u}$ transition. Attempts have been made to observe the inverse transition, $^{3}T_{1u}$ $\rightarrow$ $^{3}A_{1g}$, by maintaining the population of the long lived $^{3}T_{1u}$ state with laser excitations at 457.9, 488.0 and 514.5 nm during the absorption measurements. The effects observed in the absorption and luminescence experiments will be discussed in terms of a configuration coordinate diagram of the F center in CaO.
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This research was sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Corporation.
Author Institution: Solid State Division, Oak Ridge National Laboratory
Author Institution: Solid State Division, Oak Ridge National Laboratory