Mid-infrared emissions of Dy³⁺ ions in CaF₂

We report on a comprehensive spectroscopic study of singly Dy 3+ doped and Er 3+ ,Dy 3+ codoped calcium fluoride (CaF2) crystals for mid- infrared laser applications. The f-f transition probabilities of Dy 3+ were determined by the Judd-Ofelt theory. The stimulated-emission cross-section reaches 0.25×10 -20 cm 2 at 2.93 µm corresponding to an emission bandwidth of 350 nm. The Er 3+ → Dy 3+ energy transfer efficiency in codoped crystals is quantified. The 4.4-µm Dy 3+ emission is observed for the first time from fluoride crystals.