1. Spectra and Energy Levels of Rare Earth Ions in Crystals;Dieke,1968
2. Spectroscopic Properties of Rare Earths;Wybourne,1965
3. CRC Handbook of Chemistry and Physics;Lide,2004
4. W.T. Carnall, P.R. Fields, K. Rajnak, Spectral intensities of the trivalent lanthanides and actinides in solution. II. Pm3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, and Ho3+, J. Chem. Phys. 49 (1968) 4412.
5. Assessment of a promethium YAG laser;Krupke;J. Quant. Electron.,1972