Efficient 3.5 μm mid-infrared emission in heavily Er3+-doped fluoroaluminate glasses and its emission mechanism

Er3+-doped fluoroaluminate glasses with different concentrations were prepared by using melt-quenching method. Under a 638 nm laser diode pumping, efficient 3.5 μm emission was observed in the 18 mol% Er3+ doped sample, which was ascribed to the Er3+: 4F9/2 → 4I9/2 transition. The fluorescence properties such as radiative transition probability, energy level lifetime and branch ratio were predicted by the well-known Judd-Ofelt theory, while the emission and absorption cross-sections were calculated using the Füchtbauer-Ladenburg and McCumber theories, respectively. Both simulated and experimental results show that Er3+-doped fluoroaluminate material is a promising gain medium for 3.5 μm laser applications.