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 Tm 3   + and/or Yb 3   + /Tm 3   + 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 Tm 3   + doped samples, while an efficient 1.8   μm emission is observed by 980   nm LD in Yb 3   + /Tm 3   + co-doped samples, along with visible UC emissions. It is found that 3 F 4 state of Tm 3   + can be easily populated and then further excited to higher excited states through Yb 3   + upon 980   nm LD. Our results suggest that these Tm 3   + doped fluoride modified germanate glasses are of great significance for searching efficient mid-infrared laser materials.