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Local structure and medium range ordering of tetrahedrally coordinated Fe3+ions in alkali–alkaline earth–silica glasses

Authors
Journal
Journal of Non-Crystalline Solids
0022-3093
Publisher
Elsevier
Publication Date
Volume
353
Identifiers
DOI: 10.1016/j.jnoncrysol.2007.03.017
Keywords
  • Optical Spectroscopy
  • Absorption
  • Luminescence
  • Silicates
  • Soda-Lime–Silica
  • Medium-Range Order
  • Short-Range Order

Abstract

Abstract Tetrahedral iron (III) environments in alkali–alkaline earth–silica glasses have been studied as functions of alkali and alkaline earth cation type and Fe 2O 3 content using photoluminescence and optical absorption spectroscopies. The luminescence band centered at 13 000–15,500 cm −1 is attributed to the 4T 1(G) → 6A 1(S) transition of tetrahedral Fe 3+ ions. This band has Gaussian linewidths of 1500–3000 cm −1 but linewidths exhibit no clear compositional dependency. Ligand field strength, 10 Dq, and the Racah parameters B and C are consistent with tetrahedral Fe 3+ and here for the first time their linear variation with the alkali/alkaline earth ratio of ionic radii, cation field strengths or individual oxide basicities is demonstrated. This is attributed to the effects of near-neighbor cations on length and covalency of Fe 3+–O bonds and on host glass structure. Alkali cations stabilize Fe 3+ ions in tetrahedral coordination; stabilization increases linearly with increasing alkali ionic radius and therefore with decreasing alkali field strength. The role of alkaline earth cations in Fe 3+ stabilization in these glasses is not clear, although their effect is the inverse of that of the alkalis. The structural behavior of Fe 3+ is defined as selective, reflecting its strong local ordering effects.

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