Optical constants in the spectral range 1.5–5.5 eV are presented for the heavy rare-earth metals Gd, Tb, and Dy. The samples are thin films prepared by vacuum evaporation at pressures below 10-9 torr, and are studied in situ using a precision ellipsometric technique. The optical spectra are broadly similar but differ slightly in their temperature dependence. The optical data complement recent magneto-optic spectra, and the significance of their difference is discussed in terms of existing electronic-structure models and the microscopic origin of the two spectra.
J. L. Erskine, G. A. Blake, and C. J. Flaten, "Optical properties of Gd, Dy, and Tb," J. Opt. Soc. Am. 64, 1332-1336 (1974)