Color Centers in a Cerium-Containing Silicate Glass

Abstract

X‐ray irradiation of glass with the weight percent composition 75% SiO₂, 25% Na₂O produces color centers which absorb visible light. Cerium in the glass prevents the formation of these centers. The nature of the centers and the mechanism by which cerium prevents their formation are studied by measuring the optical absorption changes caused by irradiation of glasses containing small concentrations of Ce³⁺ and Ce⁴⁺. The conclusions are: In cerium‐free glass, trapped holes cause optical absorption bands with maxima near 4400 and 6200 Å. By capturing holes, Ce³⁺ inhibits the formation of these two bands. The probability that a hole escapes capture by Ce³⁺ is exp (—v₃c₃), where c₃ is the Ce³⁺ concentration and v₃=(9±2) × 10⁴ ų. Trapped electrons cause an optical absorption band that has a maximum in the uv and that extends to 6000 Å in the visible. Ce⁴⁺ inhibits the formation of this band by capturing electrons.