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

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.