We report on a comprehensive spectroscopic study of singly Dy3+ doped and Er3+,Dy3+ codoped calcium fluoride (CaF2) crystals for mid- infrared laser applications. The f-f transition probabilities of Dy3+ were determined by the Judd-Ofelt theory. The stimulated-emission cross-section reaches 0.25×10-20 cm2 at 2.93 µm corresponding to an emission bandwidth of 350 nm. The Er3+ → Dy3+ energy transfer efficiency in codoped crystals is quantified. The 4.4-µm Dy3+ emission is observed for the first time from fluoride crystals.
Nguyen et al. (2025) studied this question.