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Oxygen impurities in X-ray storage phosphors BaFBr and BaFCl investigated by 17O 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 17O) 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 O22- 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 O22-. Although it was intended to introduce oxygen only through BaO, 1H NMR indicates OH- on several sites. The NMR spectra, including those of 19F, 81Br and 35Cl, are compared with results obtained previously by electron paramagnetic resonance and magneto-optical techniques on 17O-containing, X-irradiated samples.