High frequency EPR spectroscopy of Er3+ ions in LiYF4 and LiLuF4: A case study of crystal fields

Abstract

We report the electronic paramagnetic resonance (EPR) studies on single crystals of LiRF4 (R = Y and Lu) doped with Er3+ ions in the frequency range of 37-1040 GHz at the liquid helium temperature. Resonance transitions between the Zeeman sublevels of three lower crystal-field Kramers doublets of Er3+ ions in magnetic fields up to 1 Tesla are registered. A prominent anisotropy of the EPR spectra in magnetic fields lying in the ab-plane of the tetragonal crystal lattice is revealed. The revised set of free-ion and crystal-field parameters for LiYF4:Er3+ and the new one for LiLuF4:Er3+ allow us to reproduce successfully the measured frequency and angular dependences of the resonant magnetic fields.