Dy³⁺-doped CaF₂-SrF₂ crystals with various Dy³⁺ dopant concentrations were synthesized by multicrucible temperature gradient technology (MC-TGT). Dy:CaF₂-SrF₂ crystals were fluorite structured and crystallized in cubic $Fm\overline{3}m$ 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⁻¹ and 12.71 cm⁻¹ were obtained at 804 nm and 1094 nm in 15% Dy:CaF₂-SrF₂ crystal. The fluorescence spectra of 15 at.% Dy:CaF₂-SrF₂ 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 Dy³⁺ dopant levels of 5%, 10% and 15%. The results indicate that the Dy:CaF₂-SrF₂ crystal is a promising candidate for compact mid-IR lasers.

Single crystals fiber (SCF) of LuAG doped with 2.0 at.% thulium has been grown by using micro-pulling down (µ-PD) technique. A continuous-wave output power of 2.44 W was achieved with a slope efficiency of 11.7% using a 783-nm diode laser as pump source. The beam quality factors M² were 1.14 and 1.67 in the x and y directions, respectively. This is, to the best of our knowledge, the first report on the Tm:LuAG SCF laser. Using ray tracing analysis, the influence of laser performance by the pump intensity distribution in the SCF was also studied.