In situ observation of the Yb 2+ emission in the radiodarkening process of Yb-doped optical preform

This Letter relates the clear evidence of Yb formation under 2.5 MeV electron irradiation in optical fiber preforms showing a darkening of the core. We thus detected by in situ photoluminescence measurements the green emission of divalent Yb under the 355 nm excitation. Moreover, we showed the existence of two types of Yb ion species with different stabilities. We demonstrated that the radiodarkening mechanism is based on a pair association of Yb with aluminum oxygen hole center point defects.