Through a Google search, my dad found a physics research paper he wrote years ago. The title: “Nuclear magnetic resonance study of the diffusion of bound and free fluorine interstitials in alkaline-earth fluorides doped with trivalent impurities.”

The abstract:

When alkaline-earth fluorides are doped with trivalent impurities, interstitial fluorines are created to maintain charge neutrality. We have performed NMR dipolar-energy relaxation measurements over a wide temperature range and have observed the diffusion of both free and locally bound fluorine interstitials F−(i) in the extrinsic region. We have observed that these motions depend strongly on the host-crystal lattice parameter. In particular, we have observed that the motion of F−(i) which is at the nearest neighbor (nn) site to the trivalent impurity dominates the relaxation above room temperature in CaF2: Y3+ but is unobserved in BaF2: Y3+. In addition, a second type of bound F−(i) motion, characterized by a much smaller activation energy, appears over a very narrow temperature range (150-185°C) in CaF2: Y3+, but over a large temperature range (below room temperature to 130°C) in BaF2: Y3+. SrF2: Y3+ shows similar behavior over a temperature range (54-160°C), which is intermediate between that of CaF2: Y3+ and BaF2: Y3+. Possible explanations in terms of the motion of a more remotely bound F−(i) [e.g., at a next-nearest-neighbor (nnn) site] and the motion of F−(i) near clusters of dipoles are discussed. We measured activation energies for all these F−(i)motions. A comparison of our results with those by other techniques (specifically, EPR, ENDOR, optical spectroscopy, ionic conductivity, ionic thermocurrent, dielectric and anelastic loss) is also given.

It's a strange feeling realizing your dad will always be smarter than you by a wide margin. I still have to teach him how to use his new Mac, though.