Efficient ∼4 µm emission from Pr³⁺/Yb³⁺ co-doped fluoroindate glass

Pr³⁺/Yb³⁺ co-doped fluoroindate (InF₃) glasses were prepared by using a traditional melt-quenching method in dry N₂ atmosphere. Pumped by a 976 or 1570 nm laser diode, efficient emissions at ∼4 µm were obtained from the Pr³⁺/Yb³⁺ co-doped glasses, which could be ascribed to the transition ³F₄ → ³H₆ of Pr³⁺ ions. The relative stimulated emission cross section was calculated to be ∼1.44 × 10⁻²⁴ m² at 4 µm, which was ∼4.2 times larger than that of transition Ho³⁺: ⁵I₅ → ⁵I₆ (3.4 × 10⁻²⁵ m²). In addition, combined with transitions ¹G₄ → ³F₃ and ¹G₄ → ³F₄ of Pr³⁺ ions, ultra-broadband emission ranging from 2.7 to 4.2 µm was also obtained. Our results indicate that Pr³⁺/Yb³⁺: InF₃ glasses could be used to develop efficient ∼4 µm lasers and widely tunable mid-infrared lasers.