Spectroscopic Studies of Ho3+-Doped SrF2 Crystal for Green and Red Laser Applications

Spectroscopic studies of Ho³⁺-doped SrF₂ crystals were performed regarding applications in solid-state lasers. The crystal structure of the Ho:SrF₂ crystal was investigated using single-crystal X-ray diffraction. SrF₂ exists as a cubic structure with an Fm3m space group. A Raman shift of 288 cm^–1 was observed for the Ho:SrF₂ single crystal. SrF₂ hosts with low-frequency vibrational modes are suitable for reducing nonradiative emissions while maximizing radiative emissions. The absorption spectrum was recorded in the visible region from 400 to 800 nm, yielding absorption lines at 416, 450, 468, 473, 484, 536, 638, and 643 nm. The fluorescence spectrum recorded at an excitation wavelength of 450 nm shows two emission bands at 546 and 656 nm, which correspond to green and red emission, respectively. The intensity parameters Ω_λ (λ = 2, 4, and 6) were estimated using the Judd–Ofelt theory. For Ho:SrF₂ single crystal, the calculated Ω_λ are Ω₂ = 0.14 × 10–20 cm², Ω₄ = 3.14 × 10^–20 cm², and Ω₆ = 3.74 × 10^–20 cm². The radiative transition probabilities, radiative lifetimes, and branching ratios β_R for Ho:SrF₂ were determined using the Judd–Ofelt parameters. The ⁵S₂ + ⁵F₄ → ⁵I₈ transition is more effective for population-building processes because of its lifetime (0.26 ms) and higher branching ratios (~82.86%). Ho:SrF₂ is, therefore, a promising solid-state laser crystal for green and red spectral regions.