An investigation of 3.5 μm emission in Er³⁺-doped fluorozirconate glasses under 638 nm laser excitation

Intense 3.5 μm mid-infrared emission has been achieved in Er³⁺-doped ZBYA glasses, which is ascribed to the Er³⁺: ⁴F_9/2 → ⁴I_9/2 transition. Based on the absorption spectrum of Er³⁺ ions, a 638 nm laser was utilized to directly pump the upper level (Er³⁺: ⁴F_9/2) to achieve 3.5 μm emission with enhanced quantum efficiency. Spectroscopic parameters were predicted by Judd-Ofelt theory. The maximum emission cross-section of the Er³⁺-doped ZBYA glass was estimated to be 5.5 × 10⁻²² cm² at 3496 nm. Additionally, the fluorescence spectra and energy level lifetimes of ZBYA glass samples with different Er³⁺ ions doping concentrations were also measured. The theoretical and experimental results confirm the potential of Er³⁺-doped ZBYA glasses for use in the development of 3.5 μm mid-infrared fiber lasers.