New Sr_1−x−zR_x(NH₄)_zF_2+x−z (R = Yb, Er) solid solution as precursor for high efficiency up-conversion luminophor and optical ceramics on the base of strontium fluoride

In this paper, we describe the use of self-fluorinating conditions for the thermal treatment of Sr_{1−x−y−z}Yb_xEr_y(NH₄)_zF_2+x+y−z precursor for the preparation of high-efficiency SrF₂:Yb:Er up-converter powders. We report actual SrF₂:Yb:Er compositions with up-conversion efficiencies exceeding 4% (pumping power 1 W/cm² at 974 nm wavelength) and describe the synthesis of ceramics with higher than 80% transmittance at 0.42–7.0 μm. The latter ceramics can be used as a potential IR radiation visualizer. For the first time, we present an analysis of correlation between up-conversion luminescence energy yield and specimen composition for SrF₂:Yb:Er nanopowders. Taking into account the observed erbium ion up-conversion luminescence in the red part of the visible spectrum, we recommend certain SrF₂:Yb:Er compositions for practical application in photodynamic cancer therapy. - Highlights: • SrF₂:Yb/Er luminophor nanopowders were precipitated from aqueous solutions. • Precipitation of Sr_{1−x−y−z}Yb_xEr_y(NH₄)_zF_2+x+y−z solid solution has been proved. • Up-conversion luminescence energy yield luminophors of more than 4% were obtained. • Optical ceramics with 80% transmittance in 0.42–7.0 μm range was synthesized.