Europium-Doped Carbonated Apatites

Abstract

In this first exploration of europium-doped carbonated apatites the location of carbonate was determined using the environment model for the analysis of IR and NMR spectra. Europium-doped carbonated apatites, containing Eu/(Eu + Ca) mole ratios of about 10%, were prepared by aqueous one-step and addition syntheses. The IR and NMR spectra of the carbonate in the samples are described using the environment model: A-type carbonate is assigned to channels containing only calcium ions (A = Ca6) or to channels containing one Na+ or a vacancy (A’ = Ca5Na or Ca5). The presence of the channel Eu3+ and the use of triammonium phosphate in the synthesis produce considerable A-type carbonate. For the apatites reported here, the carbonate is distributed in approximately a 60 to 40 ratio for channel occupancy versus replacement of phosphate. The europium is assumed to have replaced calcium ions in the Ca(II) (channel) location and the stoichiometry of the products is used to propose that, contrary to much of the Eu(III) substitution literature, the charge-balance mechanism is likely to involve the substitution of two europium ions for three calcium ion with the concomitant formation of a calcium vacancy. The environment model is also used in the correlation of the a-axial lattice parameter with the percent A-type carbonate.