EPR Spectra and Distribution of Manganese Ions in Modified Fluorozirconate Glasses

We have studied EPR spectra of MnO2-activated fluorozirconate and fluorohafnate glasses in order to determine the oxidation state and distribution of the manganese ions. The effect of activator concentration on the ratio of the percentage of free Mn4+ ions to that of ions in clusters in the glasses has been investigated for the first time. The results demonstrate that, at high activator concentrations, the manganese ions in the glasses are clustered, and only a small fraction of them are present as isolated ions. Reducing the manganese concentration leads to an increase in the percentage of free Mn4+ ions. Devitrification is accompanied by dissociation of the clusters and a transition of the ions to an isolated state.