The difference in the coordination environment around Yb³⁺ ions between Yb–Al-doped and Yb–P-doped silica glasses

To examine the difference in coordination environment around Yb³⁺ ions between Yb–Al-doped (YAS) and Yb–P-doped (YPS) silica glasses, Al/Yb dependence of the local structure around Yb³⁺ ions was investigated by EXAFS and optical measurements in YAS glasses and compared with the previous results of the P/Yb dependence in YPS glasses. It was found that Al³⁺ ions gradually coordinate to the Yb³⁺ ions with increasing Al/Yb from 0 to 20, and Yb–O coordination number changes from 4 to 8 in YAS, while in YPS glasses P⁵⁺ ions rapidly coordinate to the Yb³⁺ ions with increasing P/Yb. Contrary to the slow change of the coordination structure in YAS glass, the clustering of Yb³⁺ ions in YPS is immediately suppressed even if Al/Yb is ∼0.4. The reason must be that Yb³⁺ is easy to take local charge compensation in YAS glasses, just as charge neutralization of Al³⁺ ions in Al-doped silica glasses. The local structure model, where the mixed existence of O⁽³⁾ an Al⁽ⁿ⁾ contributes to charge compensation around Yb³⁺ ions in YAS glasses, was proposed. (author)