X-ray photoelectron spectroscopy study of sodium germanate glass containing cobalt oxide

Sodium germanate glasses containing cobalt oxide were studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (AES) and optical spectroscopy. The XPS spectra of the starting compounds such as GeO₂, Na₂CO₃ and Co₃O₄, from the melts of which glasses were prepared, were measured. The Co 2p spectra in Co₃O₄ had weak satellite lines while these were intense in the glasses. Furthermore in the glasses an increased energy separation between the Co 2p _{1 2} and Co 2p _{3 2} spin-orbit components as compared with the Co₃O₄ was observed. These observations indicated the presence of high-spin cobalt (II) ions in the glasses. Exact identification of the composition of the Co complexes in the glass is beyond the scope of present work. However, of the few possibilities considered here, the formation of the ternary oxide of Co and Ge surrounded by glass matrix has a high probability. Optical absorption spectra were consistent with these proposed structures.