Spectroscopic Analysis of Ho:BaF2 Crystals in the NIR to MIR Spectral Region

Infrared lasers in the 1-3 μm region are increasingly important for applications in medical treatment, atmospheric monitoring, and high-power laser systems. Holmium ions (Ho 3+ ) are particularly attractive because of their multiple emission channels covering near to mid infrared ranges. This work aims to systematically evaluate the structural and spectroscopic properties of Ho:BaF 2 crystals and determine the optimal doping concentrations for efficient multi-band laser operation. High-quality Ho:BaF 2 single crystals with concentrations of 0.5%-3.0% (in atom) were grown using the temperature gradient technique (TGT). Structural characterization was performed, while spectroscopic properties were analyzed *via* absorption, fluorescence, and lifetime measurements. Judd-Ofelt analysis was further applied to calculate radiative parameters. All samples exhibited cubic structures, with doping segregation ratios close to unity and uniform Ho 3+ distribution. Spectroscopic evaluation revealed optimal doping concentrations of 2.0% (in atom) for ~1.2 μm ( 5 I 6 → 5 I 8 , spectral quality factor *Q* =24.29×10 -21 cm 2 ·ms) and ~2.05 μm ( 5 I 7 → 5 I 8 , *Q* =67.53×10 -21 cm 2 ·ms), and 1.0% (in atom) for ~2.85 μm ( 5 I 6 → 5 I 7 , *Q* =44.52×10 -21 cm 2 ·ms). BaF 2 host, with its low phonon energy (~346 cm -1 ) and anti-clustering characteristics, enabled enhanced emission performance, including a maximum emission cross-section of 3.81×10 -21 cm 2 at ~2.05 μm. These results outperform traditional hosts such as YAG and CaF 2 . Compared to oxide hosts, BaF 2 offers superior lifetime, reduced non-radiative losses, and greater resistance to concentration quenching. The findings indicate that Ho:BaF 2 supports higher effective doping levels, making it particularly promising for high-power and ultrafast laser applications. Ho:BaF 2 crystals demonstrate excellent potential as efficient, multi-wavelength infrared laser gain media.