An efficient 1.8 μm emission in Tm3 + and Yb3 +/Tm3 + doped fluoride modified germanate glasses for a diode-pump mid-infrared laser

The competition between infrared down-conversion (DC) and visible up-conversion (UC) is systemically studied in Tm3 + and/or Yb3 +/Tm3 + co-doped fluoride modified germanate glasses. Based on the absorption spectra, the Judd-Ofelt intensity parameters, absorption and emission cross-sections, figure of merit (FOM), and saturated gain coefficient are calculated and analyzed. An intense 1.8 μm emission is obtained upon 808 nm laser diode (LD) excitation in Tm3 + doped samples, while an efficient 1.8 μm emission is observed by 980 nm LD in Yb3 +/Tm3 + co-doped samples, along with visible UC emissions. It is found that 3F4 state of Tm3 + can be easily populated and then further excited to higher excited states through Yb3 + upon 980 nm LD. Our results suggest that these Tm3 + doped fluoride modified germanate glasses are of great significance for searching efficient mid-infrared laser materials.