Broadband 1.20 μm emission in Tm³⁺-doped and Tm ³⁺/Tb³⁺, Eu³⁺ codoped gallogermanate glasses

Broadband 1.20 μm emission originating from the Thulium (Tm ³⁺): ¹G₄ → ³H₄ transition was observed in Tm³⁺-doped gallogermanate glasses under 476.5 nm excitation. The stimulated emission cross-section is calculated to be 2.85 × 10^-21 cm² using the Füchtbauer-Ladenburg approach. Difficulty in the population inversion between the upper 1G4 and lower 3H4 levels resulting from the cross relaxation process Tm³⁺ [¹G₄, ³H₆] → [ ³H₄, ³H₅] was overcome by the incorporation of Terbium (Tb³⁺) and Europium (Eu³⁺) ions. A Judd-Ofelt analysis was performed based on the absorption spectrum and the derived intensity parameters (Ω₂ = 4.65 × 10 ^-20, Ω₄ = 1.51 × 10^-20, and Ω₆ = 1.42 × 10^-20 cm²) reveal a strong asymmetry and covalent environment between Tm³⁺ ions and ligands in the host matrix. The results indicate that the Tm³⁺/ Tb³⁺, Eu³⁺ codoping scheme is promising in the development of amplifiers and lasers operating at the relatively unexplored 1.2 μm wavelength region.