Optical spectra of Eu3+ ion pairs in Y2O3

All the optical transitions of Eu³⁺ ions substituted on Y³⁺ lattice sites of point symmetryC ₂ orC _3i in Y₂O₃ show weak extra lines (satellites) extending over a range of few wavenumbers on both sides of the main line. It is proved by a study of the concentration dependence of the intensities of these satellites that they arise from pairs of two identical Eu³⁺ ions, interacting with each other when their separation is less then ～9 Å. By means of absorption and fluorescence excitation spectra of the transitions of Eu³⁺ at lattice sites of point symmetryC _3i , first, second and third nearestC _3i -C _3i neighbour pairs could be identified. The mean pair interaction is of the order of 5 cm^?1 and is assumed to be due to superexchange via the oxygen ions.