Doping limit and site occupation of Yb3+ in strontium fluoroapatite

Abstract

Yb³⁺ doped strontium fluoroapatite (Yb:Sr₅(PO₄)₃F) powders with various dopant concentrations were synthesized through the co-precipitation method. The XRD patterns of powders calcinated at different temperatures, combined with SEM pictures and EDS data, indicate that the limit of Yb³⁺ dopant concentration for fabricating pure-phase and stable Yb:Sr₅(PO₄)₃F powders is lower than 7%. The nonlinear relationship between dopant concentration and the full width at half minimum (FWHM) of ¹⁹F MAS-NMR spectra and ³¹P MAS-NMR spectra and the peaks located at 995 nm and 1010 nm in the emission spectra, which are assigned to Yb³⁺ ion occupation in Sr(I) sites, show that Yb³⁺ ions ocuppy both Sr(I) sites and Sr(II) sites in the Sr₅(PO₄)₃F lattice structure. The study reveals the upper limit of dopant concentration and site occupation of Yb³⁺ ions in Sr₅(PO₄)₃F powders; this is of great value for the fabrication of Yb:Sr₅(PO₄)₃F ceramics with high optical quality and laser performance.