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.