1. B. G. Wybourne, Spectroscopic Properties of Rare Earths, John Wiley, New York, 1965.
2. G. H. Dieke, Spectra and Energy Levels of Rare Earth Ions in Crystals, Ed. H. M. Crosswhite and H. Crosswhite, John Wiley, New York, 1968.
3. S. Hiifner, Optical Spectra of Transparent-Rare Earth Compounds, Academic Press, New York, 1978.
4. C. A. Morrison and R. P. Leavitt, Handbook of the Physics and Chemistry of Rare Earths, Ed. K. A. Gschneider and L. Eyring, North-Holland Publishing Co., New York, 1982, Vol. 5.
5. C. F. Fischer, The Hartree-Fock Method for Atoms, Wiley-Interscience, New York, 1977.