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Relationship between glass structure and spectroscopic properties in Er3+/Yb3+/Al3+/P5+-doped silica glasses

In this study, Er3+/Yb3+/Al3+/P5+-doped silica (simplified as EYAPS) glasses with different P/Al ratios ranging from zero to infinity were fabricated via the sol-gel method combined with high-temperature sintering. The absorption, emission and fluorescence lifetime of Yb3+ and Er3+ ions as well as the energy transfer efficiency from Yb3+ to Er3+ ions were recorded. The composition-dependent macroscopic properties were correlated to the glass structures, and probed by pulse electron paramagnetic resonance (EPR) and Raman spectroscopy. Results show that the spectral properties of Er3+ and Yb3+ ions and their local environment as well as the global glass network structure of EYAPS glasses are strongly dominated by the P/Al ratio. With the increase of the P/Al ratio, pulse EPR shows that rare earth ions gradually moved from a silicon and aluminum rich environment to a phosphorus rich environment. Raman spectroscopy shows that the maximum phonon energy of EYAPS samples gradually increases from 1200 to 1326 cm−1 due to the formation of AlPO4-like units and P = O double bonds. These structural changes lead to a gradual increase of peak absorption and emission cross sections of Er3+ ions at 1.5 µm, as well as the energy transfer efficiency of 2F5/2 level of Yb3+ to 4I11/2 level of Er3+ ions.