Optical Constants of Eight Rare Earth Elements: (Ce), (Sm), (Gd), (Tb), (Dy), (Er), (Tm), and (Yb)

Abstract

The 14 rare-earth elements or lanthanides lie in the periodic table between atomic numbers 58 and 71, cerium to lutecium, and are generally characterized by a basic electron configuration of 6s2 5d1 and the progressive filling of the 4f electron shell. The exceptions are europium, which has 7 4f electrons and none in the 5d shell, and ytterbium, which has 14 4f and no 5d. Both of these elements thus exhibit cubic structures. The rest are hexagonal and exhibit anisotropic optical properties. The optical behavior of these elements in this group between 10 and 10,000 eV is generally governed by the 3, 4, and 5d electrons as the 4f electrons lie in a narrow localized band and are shielded by the outer 5p and 6s electrons, which are in overlapping bands giving a high density of states close to the Fermi energy. This situation allows many quantum transitions between these bands and the Fermi energy at low photon energies (1 to 5 eV), thus giving rise to several absorption peaks in this spectral region.