Towards understanding of the germanate anomaly in europium–lead–germanate glasses

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Glasses in the system xEu 2O 3·(100 − x)[7GeO 2·3PbO 2] with 0 ≤ x ≤ 25 mol% have been prepared from melt quenching method. Influence of europium ions on structural behavior in lead-germanate glasses has been investigated using infrared spectroscopy and DFT calculations. The structural changes have been analyzed with increasing rare earth concentration. The general trend in the intensity of IR spectra is to increase with Eu 2O 3 content in the 700–1200 cm − 1 region, whereas the intensity in the 400–600 cm − 1 is remained almost unaffected. This suggests that the glass network modification has taken place mainly in the germanate part whereas the lead part remained unmodified and its network consists mainly from the [PbO 3] and [PbO 4] structural units. Thus, the germanate network in europium–lead–germanate glasses exists mostly as the [GeO 4] tetrahedral units, the [GeO 6] octahedral structural units and with interconnected through Ge–O–Ge bridges in [GeO 4] structural units. These europium–lead–germanate systems exhibit a photosensitive effect which can be induced through laser exposures ( λ = 633 nm) directly on the bulk sample. Structural investigations by FTIR spectroscopy show that the presence of fivefold Ge as a possible transitional phase from four to sixfold Ge was necessary. At higher content of europium oxide, the anomaly behavior of the germanium is due to the formation of small membered rings of [GeO 4] and the apparition of non-bridging oxygens. The reversion to the formation of non-bridging oxygens may thus tend to become energetically more favorable as europium oxide content increases.