Influence of Al3+ and P5+ ion contents on the valence state of Yb3+ ions and the dispersion effect of Al3+ and P5+ ions on Yb3+ ions in silica glass

Abstract

Three series of Yb³⁺-doped silica glasses containing different amounts of Al₂O₃ and P₂O₅ were prepared successfully by using a sol–gel method. Absorption, excitation and fluorescence spectra of Yb²⁺ ions in these silica glasses as well as X-ray photoelectron spectra (XPS) of Yb4d were recorded and analysed systematically. It is found out that the addition of Al³⁺ or P⁵⁺ ions has great influence on the redox state of ytterbium ions. With increasing Al³⁺ ion contents in these silica glasses, more trivalent Yb³⁺ ions are reduced to divalent Yb²⁺. In contrast, the increase of P⁵⁺ ion contents greatly promotes divalent Yb²⁺ ions to be oxidized to trivalent Yb³⁺. The possible redox mechanisms have been explored and discussed in detail. The influence of Al³⁺ and P⁵⁺ ion contents on the near-infrared luminescence intensity of Yb³⁺ ions and cooperative luminescence of Yb³⁺ ion pairs was also discussed. Both the near-infrared luminescence intensity of Yb³⁺ ions and cooperative luminescence of Yb³⁺ ion pairs decrease gradually with increasing Al³⁺ and P⁵⁺ ion contents. The decrease of cooperative luminescence of Yb³⁺ ion pairs indicates a good dispersion effect of Al³⁺ and P⁵⁺ ions on Yb³⁺ ions in Yb³⁺-doped silica glass. The results are useful for optimization of fabrication of the high quality Yb³⁺-doped silica fiber by the composite design of Yb–Al–P co-doped silica glass.