A comprehensive study of the site location of Nd3 + ions in the BaMgF 4 ultratransparent ferroelectric crystal is presented. By combining different low-temperature optical spectroscopies and electron paramagnetic resonance, the crystal field energy levels of Nd3 + ions and the gyromagnetic factors are experimentally determined. These results are employed to perform the crystal field analysis of Nd3 + ions considering a Cs point symmetry. The crystal field calculation yields a small root-mean-square deviation of 18 cm -1 and reveals a large crystal field strength (621 cm -1), verifying the assignment of the Ba2 + cationic site as the location for Nd3 + ions in this fluoride host. The results suggest a slight displacement of Nd3 + from the barium regular site with a rearrangement of the fluorine ions around it. The work gives a deep insight into the properties of the Nd3 +-doped BaMgF 4 crystal, a ferroelectric widely ultra-transparent material with potential applications as optical device operating in the Vacuum Ultraviolet-Ultraviolet and midinfrared spectral regions. © 2012 American Physical Society.