X-ray photoelectron spectroscopy study of sodium-copper-germanate glasses

Sodium germanate glasses containing copper oxide with the nominal composition (0.70 - x) GeO ₂-0.30Na ₂O-xCuO, (x in the range 0-0.15 mol%), were prepared and their structure as well as the valence state of the copper ions have been investigated by X-ray photoelectron spectroscopy (XPS). The absence of "shake up" satellite peak in the Cu 2p spectra for glasses with x = 0.05 and 0.15 suggests the presence of copper in the Cu ⁺ state for these glasses while the presence of both oxidation states (Cu ⁺ and Cu ²⁺) in the glass with x = 0.10 has been concluded from the presence of satellite structure of the Cu 2p core level spectra as well as the observation of asymmetry in the Cu 2p spectra. A deconvolution procedure has been undertaken to determine quantitatively the Cu ²⁺/Cu _total ratio for x = 0.10 glass composition. The non-bridging oxygen content, obtained from the deconvolution of the O 1s core level spectra, increases with increasing copper oxide content indicating that copper acts as a network modifier. The Ge 3d core level spectra show asymmetry and were fitted with two contributions, one due to Ge atoms in Ge (IV) coordination and the other due to Na 2p core level spectra which were overlapping with the Ge 3d peaks.