On the role of Yb as an impurity in the excitation of Er3+ emission in silicon-rich silicon oxide

The aim of this work is to check if Yb3+ ions can be used as sensitizers for the 4I13/2–4I15/2 emission of Er3+ ions at 1.54 μm in silicon-rich silicon oxide (SRSO). To answer this question, photoluminescence excitation (PLE) experiments were performed on the Er3+ emission in a wide range of excitation wavelengths. The PLE spectra in the 420–650 nm range were excited using an optical parametric oscillator. In Er + Yb implanted silica we found an absorption band related to Yb at wavelengths shorter than 530 nm. Radiation defects were excluded as absorbing species in this range of wavelengths. In SRSO PLE by Yb is entirely suppressed by absorption due to silicon nanoclusters. As a result we conclude that Yb doping of SRSO:Er does not improve the PL efficiency of Er3+ in comparison with SRSO:Er. We interpret a sensitization mechanism by Yb in the UV-green range in terms of the Yb2+ → Yb3+ recharging process, in which an Yb ion becomes excited into its 2+ state, leaving a hole, hVB, localized near Yb2+. Recombination with a hole leaves Yb3+ in its 2F5/2 excited state from which energy is very efficiently transferred to Er3+ ions.