Role of Cerium in Suppression of Gamma‐Ray Induced Coloring of Borate Glasses

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Abstract
The role of cerium in the suppression of gamma‐ray induced coloration in glass has been found to depend on the relative concentration of Ce 3+ to Ce 4+ ions as well as on the total cerium content. In a borate glass having high ultraviolet transmission, it has been found that both Ce 3+ and Ce 4+ ions are necessary to suppress the optical absorption bands induced in the visible region. The role of cerium can be explained on the basis of a change in its oxidation state as a result of gamma irradiation. It is postulated that the cerous ions, by the reaction Ce 3+ → Ce 4+ + e , suppress the induced visible band at 2.36 ev (525 mμ), which may result from positive hole centers. High cerous ion concentration results, however, in an induced center (Ce 3+ + e ) which absorbs in the visible at about 1.9 ev (650 mμ). The presence of Ce 4+ ions near Ce 3+ prevents the formation of this center possibly by the reaction Ce 4+ + e → Ce 3+ . These induced opposite changes in the oxidation state of cerium tend to maintain a balance in the ratio of Ce 3+ to Ce 4+ ions in the glass during irradiation, and the suppression of the visible bands depends on this ratio.

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