Anomalous behavior of the F19 motional relaxation in PbF2 doped with alkali halides
Abstract The F 19 motional relaxation in PbF 2 doped with alkali halides is studied as a function of temperature and frequency using nuclear magnetic resonance. The results of spin lattice relaxation rate measurements in the rotating frame and in the laboratory frame are reported and some striking anomalies are pointed out. We propose that these anomalies, not accountable by a straightforward application of the predictions of the Bloembergen-Purcell-Pound theory, arise from a non-uniform mobility of fluorine atoms around the impurities. A model that attempts to explain some of these discrepancies is discussed.