OXYGEN IMPURITIES IN X-RAY STORAGE PHOSPHORS BAFBR AND BAFCL INVESTIGATED BY O-17 NMR

Magic-angle-spinning nuclear magnetic resonance (NMR) spectroscopy of BaFBr and BaFCl doped with up to 6 mol.% oxygen (previously enriched to 40% in O-17) has detected sites on which oxygen impurities were incorporated. In BaFBr:O, monatomic O2- is found preferentially on fluoride sites, and subsidiarily on bromide sites, but in BaFCl:O, substitutional O2- falls below the threshold of detection. In both systems the diamagnetic molecular anion O2(2-) is detected, on one site in BaFBr:O, on two in BaFCl:O; one of the latter is assigned to the chloride site, while the other is attributed to interstitial O2(2-). Although it was intended to introduce oxygen only through BaO, H-1 NMR indicates OH- on several sites. The NMR spectra, including those of F-19, Br-81 and Cl-35, are compared with results obtained previously by electron paramagnetic resonance and magneto-optical techniques on O-17-containing, x-irradiated samples.