Crystal field strength in C-type cubic rare earth oxides

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 D-5(0) to F-7(0-4) levels of the ground F-7 multiplet were observed between 575 and 720 nm. The complete lifting of the F-7(J) level degeneracy as well as the absence of transition selection rules imposed by the group theory are consistent with the C-2 point symmetry of the RE3+ site. Only a few lines originating from Eu3+ ions in the high symmetry S-6 site were observed. The crystal field (c.f.) analysis conducted on the basis of the 18-21 F-7(0-4) c.f. levels yielded satisfactory results despite the high number (14) of the B-q(k) and S-q(k) 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. (C) 2002 Elsevier Science B.V. All rights reserved.