Enhanced 27 μm mid-infrared emissions of Er^3+ via Pr^3+ deactivation and Yb^3+ sensitization in LiNbO_3 crystal

The use of Pr³⁺ codoping for enhancement of the transition of Er³⁺: ⁴I11/2 → ⁴I13/2 2.7 μm emissions was investigated in the Er/Yb codoped LiNbO₃ crystal for the first time. It is found that the codoped of Pr³⁺ ion in Er³⁺, Yb³⁺ and Pr³⁺ triply doped LiNbO₃ crystal (Er/Yb/Pr: LN) greatly enhances Er³⁺: 2.7 μm emission under excitation of a common 970 nm laser diode, depopulates the lower laser level of Er³⁺:⁴I13/2, and has little influence on the higher laser level of Er³⁺:⁴I11/2 at the same time for population inversion. The 2.7 μm emission characteristics and energy transfer were investigated in detail. The energy transition efficiency from lower laser level of Er³⁺:⁴I13/2 to Pr³⁺:³F₄ level is as high as 0.42, indicating that the Pr³⁺ ion is an effective deactivation ion for Er³⁺ ion in LiNbO₃ crystal. These results suggest that Er/Yb/Pr: LiNbO₃ crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 970 nm LD pump.