Spectroscopy of Yb3+ ions in multisite MgMoO4 crystal

• Yb 3+ -doped magnesium monomolybdate crystal is grown by the Czochralski method. • Yb:MgMoO 4 belongs to the monoclinic class (space group C 2/ m ). • The stimulated-emission cross-section for Yb 3+ ions is 0.76 × 10 –20 cm 2 at 1031 nm. • Yb 3+ ions in MgMoO 4 present at least eight non-equivalent optical centers. • The multi-site behavior induces a strong inhomogeneous spectral line broadening. Yb 3+ -doped magnesium monomolybdate crystal (Yb:MgMoO 4 ) is grown by the Czochralski method. The crystal structure, thermal expansion, vibronic properties, polarized room- and low-temperature spectroscopy of this new compound were studied. According to the Rietveld refinement, Yb:MgMoO 4 belongs to the monoclinic class (sp. gr. C 2/ m , lattice constants: a = 10.276(9)Å, b = 9.289(6)Å, c = 7.027(6)Å and β = 106.903(8)°). The highest-energy Raman mode of Yb:MgMoO 4 is found at 969 cm -1 and assigned to symmetric stretching vibrations of [MoO 4 ] 2- tetrahedra. Yb 3+ ions in MgMoO 4 exhibit intense and broad absorption at 978 nm, relatively broad and smooth emission bands above 1 μm (stimulated-emission cross-section: σ SE = 0.76 × 10 –20 cm 2 at 1031 nm for light polarization E || c ) and a long luminescence lifetime (0.63 ms). The low-temperature (12 K) spectroscopic studies evidenced a multi-site behavior for Yb 3+ ions in MgMoO 4 revealing at least 8 non-equivalent optical centers which are assigned to different charge compensation mechanisms. This induces a strong inhomogeneous spectral line broadening. For envisioned laser applications, the problem of low Yb 3+ segregation coefficient ( K Yb ∼0.029) needs to be solved.