Growth and optical properties of ytterbium and rare earth ions codoped CaF2-SrF2 eutectic solid-solution (RE = Y3+, Gd3+, La3+)

Ytterbium and rare earth ions (RE = Y, Gd, La) codoped CaF2-SrF2 single crystals (3 at% Yb,6 at% RE:CaF2-SrF2) were fabricated by temperature gradient technology (TGT). All the space groups remain the same Fm3m as that of Yb:CaF2-SrF2. The lattice parameter a, unit cell volume V, as well as bond length of Ca/Sr–F and F–F increase in the sequence of rare-earth ions radius Y3+ < Gd3+ < La3+. The segregation coefficients of Yb ions are 0.87 in Yb,La:CaF2-SrF2 and Yb,Gd:CaF2-SrF2, which are larger than 0.85 in Yb,Y:CaF2-SrF2 and 0.80 in Yb:CaF2-SrF2. Absorption spectra in the range of 200 and 400 nm were analysed with Yb2+ contents. The absorption and emission cross-sections in the range of 900–1100 nm were determined together with fluorescence lifetime. The saturation pump density Isat, minimum pump density Imin and gain cross-section σg were analysed. Yb,La:CaF2-SrF2 has a relatively higher optical parameter (σem × τ, 0.52 × 10−20 cm2 ·ms), lower Isat (3.68 kW/cm2) and Imin (0.50 kW/cm2) at 1038 nm indicating the potential application in high power laser. Low phonon energy of CaF2-SrF2 is 302 cm−1 which is located between those of CaF2 and SrF2 as measured by Raman spectra. It is believed that ytterbium and rare earth ions (RE = Y3+, Gd3+, La3+) codoped CaF2-SrF2 eutectic solid-solution is promising for high-power and wavelength-tunable solid-state lasers.