| Summary: | Dy<sup>3+</sup>-doped CaF<sub>2</sub>-SrF<sub>2</sub> crystals with various Dy<sup>3+</sup> dopant concentrations were synthesized by multicrucible temperature gradient technology (MC-TGT). Dy:CaF<sub>2</sub>-SrF<sub>2</sub> crystals were fluorite structured and crystallized in cubic <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>F</mi><mi>m</mi><mover accent="true"><mn>3</mn><mo>¯</mo></mover><mi>m</mi></mrow></semantics></math></inline-formula> space group, as characterized by X-ray diffraction. The crystallographic site concentration was calculated from the measured density by Archimedes’ hydrostatic weighing principle. The optical transmission reached over 90% with a sample thickness of 1.0 mm. The Sellmeier dispersion formula was obtained following the measured refractive index in a mid-IR range of 1.7–11 μm. Absorption coefficients of 6.06 cm<sup>−1</sup> and 12.71 cm<sup>−1</sup> were obtained at 804 nm and 1094 nm in 15% Dy:CaF<sub>2</sub>-SrF<sub>2</sub> crystal. The fluorescence spectra of 15 at.% Dy:CaF<sub>2</sub>-SrF<sub>2</sub> showed the strongest wavelength peak at 2919 nm with a full width at half maximum (FWHM) of 267 nm under an excitation wavelength of 808 nm. The fluorescence lifetimes were illustrated for different Dy<sup>3+</sup> dopant levels of 5%, 10% and 15%. The results indicate that the Dy:CaF<sub>2</sub>-SrF<sub>2</sub> crystal is a promising candidate for compact mid-IR lasers.
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