Optical absorption in Co-doped SiO2-GeO2 glass rods and fibers

Optical absorption spectra in rods and fibers of Co-doped SiO2-GeO2 glass have been studied comparatively, and the result is extended to other transition-metal ions. In the glass with a high-Co concentration (approximate to2000 wt. ppm), absorption peaks due to Co2+ ions appear differently in the rod and the fiber. A deconvolution analysis shows that this difference arises from the ratio of CoO4 and CoO6 units, the latter being preferred in the rod. This observation can be understood in terms of fictive temperature and free energy. The thermodynamical idea is also applied to the coordination behavior of other transition-metal ions in oxides, which suggests a close correlation between glasses and crystals. Results for a low-Co-concentration glass are also discussed. (C) 2003 American Institute of Physics.