Reduction of Eu3+ to Eu2+ in aluminoborosilicate glasses under ionizing radiation

Eu2O3-doped aluminoborosilicate glasses were prepared by melting in air at high temperature (∼1500 oC). It was shown by luminescence and Electron Paramagnetic Resonance (EPR) measurements that both Eu3+ and Eu2+ ions can exist simultaneously in the glass matrix studied after glass synthesis as well as after exposure to ionizing radiation. Increase of total Eu2O3 concentration leads to the increase of Eu3+ luminescence intensity while the luminescence intensity of Eu2+ ions tends to decrease. In contrast the EPR indicates that the amount of Eu2+ ions in the glass increases with total Eu2O3 concentration. The difference in the results of the two spectroscopies is explained in terms of energy transfer from Eu2+ to Eu3+ leading to an Eu2+ luminescence quenching. Irradiation results in the increase of reduced Eu2+ quantity detected by EPR measurements. It was shown that Eu2+ ions are located in both high (g ∼ 4.6) and low symmetry ('U' spectrum) sites in the structure of aluminoborosilicate glasses. The increase of Eu2+ content by the increase of the irradiation dose manifests the strong reduction process Eu3+ → Eu2+.