Homogeneity of doping with paramagnetic ions by NMR

Abstract

In NMR, paramagnetic dopants change the relaxation behavior and the chemical shift of the nuclei in their immediate environment. Based on the concept that the “immediate environment” in a diamagnetic host material can be described as a sphere with radius r₀, we developed a function for the fraction of unperturbed nuclei (the fraction of nuclei outside the sphere) which gives a link between the effective radius and the doping concentration. In the case of a homogeneous doping scenario a characteristic dependence is observed in both theory and experiment. We validated the model on a sample series where paramagnetic Eu(II) ions are doped into crystalline SrH₂. The fraction of unperturbed nuclei was determined from the ¹H NMR signal and follows the predicted curve for a homogeneous doping scenario where the radius r₀ is 17 Å.