Crystal field energy level scheme of Er3+ in GdOCl Parametric analysis

Abstract

The optical absorption spectra of the trivalent erbium ion (Er 3+ ) in polycrystalline GdOCl (x Er = 0.09) samples were measured from 200 to 1650 nm at selected temperatures between 9 and 300 K. The luminescence from the 4 S 3/2 and 4 F 9/2 levels in GdOCl:Er 3+ (x Er = 0.02) was also observed at 77 K under argon-ion laser excitation in the region between 540 and 870 nm. The interpretation of the absorption and emission spectra yielded an energy level scheme consisting of 17 2S+1 L J levels; i.e. 61 Stark components out of the 182 Kramers doublets for the 4f 11 configuration. This scheme was fit to a Hamiltonian of 19 adjustable parameters including the free ion [Racah (E 0–3 ), Trees (α, β, γ) and Judd (T k ; k = 2–4, 6–8) parameters as well as the spin–orbit coupling constant (ζ 4f )] together with the crystal field B q k (B 0 2 , B 0 4 , B 4 4 , B 0 6 and B 4 6 ) parameters according to the C 4v point group symmetry of the Er 3+ site in the tetragonal lanthanide (Ln) oxychloride. The experimental energy level scheme was reproduced with a satisfactory root-mean-square deviation equal to 19 cm −1 . The present results were found consistent with the energy level parametrisation of Pr 3+ (4f 2 ) in PrOCl, Nd 3+ (4f 3 ) in NdOCl, Tb 3+ (4f 8 ) in TbOCl as well as of Eu 3+ (4f 6 ) and Tm 3+ (4f 12 ) in GdOCl. The influence of the nuclear charge, the energy of the 5s (and 5d) orbitals and the two-electron crystal field terms are discussed as possible interactions responsible for the evolution of the B q k parameters along the Ln series.