1. Nakamura S. Pearton S. J. Fasol G. , The Blue Laser Diode: The Complete Story, 2nd edition, Springer (2000).
2. Hufner S. , Optical Spectra of Transparent Rare Earth Compounds, Academic, New York (1978).
3. Aharoni A. , Introduction to the Theory of Ferromagnetism, 2nd edition, Oxford Science Publications (2000).
4. Van Vleck J. H. , “ Theory of Electric and Magnetic Susceptibilities ”, Chap. XII, Oxford (1932).
5. For a list of the effective magnetic moments of the RE3+ ions, see Lide D. R. , CRC Handbook of Physics and Chemistry (2004).