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

Broadband 1.20 μm emission originating from the Thulium (Tm3+): 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.

► The first observation of 1.20 μm emission from Tm3+: 1G4 → 3H4 transition in gallogermanate glasses.
► The population inversion for Tm3+: 1G4 → 3H4 transition is achieved by codoping of Tb3+ and Eu3+.
► Cross relaxation processes are responsible for the depleting of the terminal level Tm3+: 3H4.
► Judd–Ofelt analysis reveals a strong asymmetry and covalent environment between Tm3+ and ligands.