Local Structures of Bismuth Ion in Bismuth-Doped Silica Glasses Analyzed Using Bi LIII X-Ray Absorption Fine Structure
Local structures around a bismuth ion in bismuth-doped silica glasses (BiSG) are analyzed using a Bi LIII X-ray absorption fine structure (XAFS). The XAFS spectrum of crystalline α-Bi2O3 was also measured for comparison with BiSG whose first peaks are about 0.1 Å less than α-Bi2O3 in radial structure functions. According to curve-fitting results using FEFF 8.2, the Bi–O distances of the first and second neighboring coordination spheres are estimated to be 2.1 and 2.3 Å, respectively. The former corresponds to Bi5+–O bonding and the latter to Bi3+–O bonding compared with the Bi–O distances in typical crystals including Bi3+ and Bi5+ ions. The above results show that Bi ions in BiSG exist as both Bi3+ and Bi5+ states, which is also supported by X-ray absorption near the edge structure spectra of BiSG.
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