Magnetic Resonance Studies of Vacancy Centers in Ionic Crystals

Abstract

The application of magnetic resonance techniques to the study of paramagnetic centres has greatly improved our understanding of point defects. In fact ESR (Electron Spin Resonance) and especially ENDOR (Electron Nuclear Double Resonance) come close to what one may call an atomic scale microscopy of paramagnetic centres. In favourable cases one obtains a very detailed picture of the atomic structure of a defect (lattice site, neighbours, symmetry) including information about lattice distortions around the vacancy or the paramagnetic impurity, as well as detailed information about the electronic structure of the centre. This very precise picture of the paramagnetic defect is mainly the result of a careful determination of the strong hyperfine interaction (hf) between the unpaired centre electron and the centre nuclei as well as the weaker hf interaction with the nuclei of the surrounding lattice ions, (sometimes called “superhyperfine interaction”, shf). In order to determine the latter, ENDOR measurements usually have to be performed, since they allow a much higher resolution of hf interactions compared to ESR measurements. Vacancy centres mostly contain no centre nuclei so that the shf interactions must be determined.KeywordsQuadrupole InteractionIonic CrystalAlkali HalideENDOR SpectrumOrder Perturbation TheoryThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.