ESR studies of iron-containing lithium, sodium and potassium silicate glasses before and after Irradiation with γ- and X-rays

Abstract

Lithium, sodium and potassium silicate glasses containing different Fe2O3 amounts were irradiated with γ- and X-rays and investigated by using ESR. The well-known iron resonances at g = 4.2 and g = 1.99 show a characteristic behaviour at the transition from lithium to potassium and by changing the Fe2O3 concentration. The resonance at g = 4.2 decreases from lithium to potassium, whereas the resonance at g = 1.99 increases. The concordance of the intensity course of the two resonances with the preference of the alkali metals to take tetrahedral or octahedral coordination is an interesting support for the attribution of g = 4.2 to 4-fold coordinated Fe3+ and g = 1.99 to 6-fold coordination of this ion. γ- and X-rays induce the same defect centres (colour centres). These centres are characterized by a strong resonance at g = 2.01. All radiation defects have a strong dependence on the type of alkali metal - they increase from lithium to potassium - and on the Fe2O3 concentration of the glasses. In glasses which contain a very small quantity of Fe2O3 the irradiation induces more defects than in the corresponding iron-free glasses. With increasing Fe2O3 content the glasses become more resistant against irradiation and at a high concentration no more defects can be produced.