3.5 μm emission in Er³⁺ doped fluoroindate glasses under 635 nm laser excitation

Under 635 nm laser excitation, the 3.5 μm luminescence, corresponding to the Er³⁺: ⁴F_9/2 → ⁴I_9/2 radiation transition, was demonstrated in Er³⁺ doped fluoroindate glasses prepared by melt-quenching method. The energy transfer mechanisms were investigated and the 3.5 μm emission intensity reached a maximum for an Er³⁺ concentration of 9 mol%. The Er³⁺ energy level lifetimes in fluoroindate glass samples were measured, their oscillator strength parameters were calculated by Judd-Ofelt theory and their emission cross-section at 3.5 μm was obtained. The maximum emission cross-section at 3.51 μm was 4.86 × 10⁻²² cm², which indicated that Er³⁺ doped fluoroindate glass is a potential gain medium for lasing at 3.5 μm.