In this paper, we describe the use of self-fluorinating conditions for the thermal treatment of Sr1-x-y-zYbxEry(NH4)(z)F2+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/cm(2) at 974 nm wavelength) and describe the synthesis of ceramics with higher than 80% transmittance at 0.42-7.0 mu m. 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. (C) 2016 Elsevier B.V. All rights reserved.