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

Abstract

In this study, Er 3+ /Yb 3+ /Al 3+ /P 5+ -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 Yb 3+ and Er 3+ ions as well as the energy transfer efficiency from Yb 3+ to Er 3+ 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 Er 3+ and Yb 3+ 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 AlPO 4 -like units and P = O double bonds. These structural changes lead to a gradual increase of peak absorption and emission cross sections of Er 3+ ions at 1.5 µm, as well as the energy transfer efficiency of 2 F 5/2 level of Yb 3+ to 4 I 11/2 level of Er 3+ ions.