Co-precipitation synthesis of highly sinterable Yb:Sr5(PO4)3F powder for transparent ceramics

2 at.% Yb:Sr 5 (PO 4 ) 3 F nanoparticles were synthesized by co-precipitation method. By using XRD , FT-IR and FE-SEM measurements, the influence of reactive conditions, including pH value, reactive temperature and mixing mode on the phase composition and microstructure of these nanoparticles were investigated. The results showed that pure Yb:Sr 5 (PO 4 ) 3 F nanopowders were produced by adding sodium hydroxide solution into S-FAP emulsion under alkaline environment or neutral environment. Agglomeration degree of the nanoparticles decreases and then increases with the increase of pH value and the aggregation was lowest when the pH value was 12. Spherical or nearly spherical nanoparticles with mean size of 24.0 nm were obtained in the environment of 20 °C and pH = 12. TEM results showed that the powders produced by fast mixing model (fast stirring and fast mixing) have more homogenous microstructure. The Yb:Sr 5 (PO 4 ) 3 F ceramic with a transmittance of 45% at 1500 nm was fabricated by hot-pressing the synthesized nanopowders. SEM results showed that residual pores and unsintered second phase are the main scattering sources of the as-prepared Yb:S-FAP ceramics.