Intense mid-infrared emission at 3.9 µm in Ho³⁺-doped ZBYA glasses for potential use as a fiber laser

Intense mid-infrared emission at 3.9 µm in Ho³⁺-doped ZBYA glasses with direct upper laser level (Ho³⁺ : ⁵I₅) pumping at a wavelength of 888 nm is reported for the first time, to the best of our knowledge. Spectroscopic parameters were determined using the Judd–Ofelt theory and the measured absorption spectrum. The maximum emission cross section of the Ho³⁺-doped ZBYA glass is estimated to be 2.7 × 10⁻²¹ cm² at 3906 nm. Additionally, fluorescence spectra and lifetimes of ZBYA glasses with different Ho³+ ion doping concentrations were measured. The results provide theoretical and experimental basis for better selection of rare-earth-doped matrix glasses to achieve a fluorescence output centered on a wavelength of 3.9 µm.