1. Spectroscopic Properties of Rare Earths;Wybourne,1965
2. Electron Paramagnetic Resonance in Compounds of Transition Elements;Altshuler,1974
3. Spectroscopic properties of triply ionized lanthanides in transparent host crystals;Morrison,1982
4. Ligand Field Theory and its Applications;Figgis,2000
5. The Effective Crystal-field Potential;Mulak,2000