Crystal field strength in C-type cubic rare earth oxides

Abstract

Luminescence of the Eu3+-doped cubic C-type rare earth (RE) oxides, RE2O3:Eu3+ (RE=Eu, Gd, Lu, Y, In and Sc) powder samples at 77 and 298 K was investigated under UV, argon ion and dye laser excitation. Intense transitions from the 5D0 to 7F0–4 levels of the ground 7F multiplet were observed between 575 and 720 nm. The complete lifting of the 7FJ level degeneracy as well as the absence of transition selection rules imposed by the group theory are consistent with the C2 point symmetry of the RE3+ site. Only a few lines originating from Eu3+ ions in the high symmetry S6 site were observed. The crystal field (c.f.) analysis conducted on the basis of the 18–21 7F0–4 c.f. levels yielded satisfactory results despite the high number (14) of the Bkq and Skq parameters. The strength of the c.f. effect increases in the RE series with decreasing ionic radius of the RE3+ host cation. This results from the increased electrostatic effect of the host lattice on the Eu3+ ion.