A comprehensive study of the site location of Nd${}^{3+}$ 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 Nd${}^{3+}$ ions and the gyromagnetic factors are experimentally determined. These results are employed to perform the crystal field analysis of Nd${}^{3+}$ 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 Ba${}^{2+}$ cationic site as the location for Nd${}^{3+}$ ions in this fluoride host. The results suggest a slight displacement of Nd${}^{3+}$ 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 Nd${}^{3+}$-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.

• Received 30 March 2012

DOI:https://doi.org/10.1103/PhysRevB.85.184110