Optical and X-ray photoelectron spectroscopy of PbGeO₃ and Pb₅Ge₃O₁₁ single crystals

摘要

Pb₅Ge₃O₁₁ crystals are found to exhibit pale yellow colouration while PbGeO₃ are colourless. X-ray photoelectron spectroscopy (XPS) measurements show lead deficiency in both the crystals. The results also reveal a stronger ionic character for PbGeO₃ as compared to Pb₅Ge₃O₁₁ crystal. The binding energy of Ge3d core level in the case of Pb₅Ge₃O₁₁ crystal is found to be smaller than the binding energy of germanium oxide, thereby indicating the incomplete oxidation of Ge ions in the crystal lattice. On gamma ray irradiation, the transmission of both the crystals is observed to deteriorate uniformly over the entire wavelength range, which has been attributed to the oxidation of some of the lattice Pb ions. On gamma irradiation the changes observed in O1s core level energies for both the crystals are seen to be consistent with the changes noted in the Pb4f _7/2 and Ge3d spectra. Interestingly, the results reveal oxidation of surface Ge atoms with atmospheric oxygen under gamma irradiation.