1. L.C. Thompson, in: K.A. Gschneider, L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, 3, Elsevier (North Holland publishing Co.), Amsterdam, 1979, p. 209.
2. W.T. Carnall, in: K.A. Gschneider, L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, 3, Elsevier (North Holland publishing Co.), Amsterdam, 1979, p. 171.
3. Radiative and non-radiative transitions of rare-earth ions in glasses
4. Analogies and Differences Between Monatomic Entities and Condensed Matter
5. G. Blasse, in: K.A. Gschneider, L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, 4, Elsevier (North Holland publishing Co.), Amsterdam, 1979, p. 237.