We describe an experimental technique for associating the satellite lines in a rare earth optical spectrum caused by a defect with the rare earth ions in crystal sites around that defect. This method involves measuring the hyperfine splitting caused
by a magnetic dipole-dipole interaction between host ions and a magnetic defect. The method was applied to Ce3+:EuCl3.6H2O to assign 13 of the outermost 22 satellite lines to sites. The assignments show that the optical shift of a satellite line is loosely dependent on the distance to the dopant. The interaction between host and dopant ions is purely dipole-dipole at distances greater than 7 Angstroms, with an additional contribution, likely superexchange, at distances less than 7 Angstroms.
