BaF2 modified Cr3+/Ho3+ co-doped germanate glass for efficient 2.0 μm fiber lasers

The influence of BaF2 on the physical and spectroscopic properties of Cr3+/Ho3+ co-doped germanate glass is investigated systematically by differential scanning calorimeter, excitation and emission spectra, as well as dynamic decay lifetime. The intense and broad absorption band of Cr3+ provides a selective pump scheme for obtaining an efficient 2.0 μm emission of Ho3+, the OH− absorption coefficient, on the other hand, is decreased as low as 1.08 cm−1, which both highly conducive to obtain an intense 2.0 μm emission of Ho3+. In addition, the crystal-field parameter Dq/B of Cr3+-doped glasses is also calculated to study the influence of BaF2 on the local environment of activators and sensitizers. Further theoretic calculation shows that the largest absorption and emission cross-sections of Ho3+ near 2.0 μm are as high as 4.6 and 5.2 (× 10−21 cm2) in the 10 mol% BaF2 modified Cr3+/Ho3+ co-doped glass and the maximum energy transfer efficiency from Cr3+ to Ho3+ is about 42.5%. All results suggest that this BaF2 modified Cr3+/Ho3+ co-doped glass is very suitable for a high-efficient 2.0 μm fiber lasers with flexible pump sources.