Near-infrared luminescence properties of Yb3+ doped LiLa(PO3)4 powders

Polycrystalline powders of condensed polyphosphate LiLa(1−x)Ybx(PO3)4 (x=5, 10, 15, 20 at%) were synthesized by solid-state reaction and characterized by a combination of powders X-ray diffraction and vibrational spectroscopies. The obtained powders crystallize in the monoclinic system with space group C2/c, characteristic ribbons of (PO4)− tetrahedrons and well separated Yb3+ ions. The Near Infrared (NIR) absorption, fluorescence spectra as well as decay curves of Yb3+ in LiLa(PO3)4 (LLP) were measured at room temperature. The absorption and emission cross sections were calculated from the absorption spectra in order to assess their capabilities of being used as laser active medium. The influence of the self-absorption at 976 nm was revealed by the little difference between the line shape of fluorescence and the calculated emission line. The decay curves of the 2F5/2 level of Yb3+ ions exhibit a single exponential nature for all the concentrations. No quenching effect was found and the lifetimes of the 2F5/2 level increase from 0.6 to 1.6 ms when the Yb3+ concentration increased from 5 to 20 mol%. The NIR spectroscopic properties were evaluated and discussed as a function of Yb3+ concentration, chemical composition and structural characteristics of LLP. The obtained results are compared to those of other reported Yb3+-doped compounds.