Quaternary doping to improve 1.5 μm quantum efficiency of Er3+ in CaF2 single crystal

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+: CaF2 single crystal was demonstrated to have high fluorescence yield in the 1.5 μm region. Through a simplified model, the branching ratio of the Er3+ 4I11/2→4I13/2 transition was estimated to be improved more than 40 times by the deactivating effect of Ce3+ in the quaternary-doped CaF2 crystal with dopants of 0.2-at% Er3+ and 2.0-at% Ce3+. Owing to the broad emission bandwidth and large emission cross-section, the quaternary-doped CaF2 system shows the great potential to achieve the high laser performance in the 1.5 μm region.