Spectroscopic properties and energy transfer in Yb3+–Ho3+ co-doped germanate glass emitting at 2.0 μm

A new kind of germanate glass co-doped with Yb3+–Ho3+ was prepared. The J-O parameters were calculated to be Ω2 = (6.59 ± 0.21) × 10− 20 cm2, Ω4 = (2.77 ± 0.36) × 10− 20 cm2, and Ω6 = (1.90 ± 0.25) × 10− 20 cm2. The little overlap between the absorption cross section and stimulated emission cross section indicates a non-resonant energy transfer process. The calculation demonstrates that the energy transfer between Yb3+ and Ho3+ is one-phonon assisted in a great measure. The gain coefficient of Ho3+ at 2.0 μm was also calculated. The fluorescence measurement shows the Yb3+ co-doping enhances the 2.0 μm emission remarkably.