Enhanced 2.75 µm emissions of Er3+ via Eu3+ deactivation in PbF2 crystal

The use of Eu³⁺ codoped for the enhancement of the transition of Er³⁺: ⁴I_11/2→⁴I_13/2 ~2.75 µm emissions was observed in the Er/Eu co-doped PbF₂ crystal for the first time. The ~2.75 µm energy transfer mechanism and fluorescence emission properties of the Eu/Er co-doped PbF₂ crystal were investigated at length. The results show that the codoped of Eu³⁺ ion in Er/Eu: PbF₂ crystal greatly enhances Er³⁺:2.75 µm emission under excitation of a common 970 nm laser diode. In addition, it is found that the Eu³⁺ ion depopulates the lower laser level of Er³⁺:⁴I_13/2, and has little effect on the upper laser level of Er³⁺:⁴I_11/2 at the same time. Moreover, the energy transfer efficiency from the Er³⁺:⁴I_13/2 level to the Eu³⁺:⁷F₆ level is as high as 88.07%, indicating that the Eu³⁺ ion is an effective deactivation ion for enhancing the ~2.75 µm emission in Er/Eu: PbF₂ crystal. These advantageous spectroscopic characteristics suggest that the Er/Eu: PbF₂ crystal may be a promising material for ~2.75 µm mid-infrared lasers under the pump of a conventional 970 nm LD.