The potentiality of Rutherford backscattering spectrometry, used in channeling mode, to locate ions in laser crystals is tested by studying the case of trivalent rare earth active ions in LiNbO3 crystals. It is shown that these active ions occupy Li+ sites but off-centered from the regular lithium position by different amounts. These displacements are directly related to the ionic radii of the active ions. First evidence of multicenter structure obtained by RBS/channeling is reported for Pr3+ ions in LiNbO3. Taking advantage of this multicenter structure the crystal field parameter can be experimentally obtained for each center. Thus, it is shown how small variations of crystal field parameters, as a consequence of the non-equivalent centers, account for features observed in the optical spectra of Nd3+ ions in this crystal. © 1997 Elsevier Science B.V.