High-Frequency Electron Paramagnetic Resonance of Tm3+ Ions in Lanthanum and Thulium Ethylsulphate Single Crystals.

Abstract

We have observed electron paramagnetic resonance and far-infrared absorption of the transitions between the singlet ground state and the first excited doublet of the Van Vleck paramagnetic ${\mathrm{Tm}}^{3+}$ ion in ethylsulphate crystals in fields up to 10.5 T. The interaction of the Stark levels with a phonon state is clearly shown. The EPR of ${\mathrm{Tm}}^{3+}$ in the 1000--1600 GHz range are single Lorentzians in lanthanum ethylsulphate but are asymmetric and richly structured in thulium ethylsulphate. This work illustrates the usefulness of high-frequency EPR in the study of Van Vleck paramagnets, which are inaccessible by EPR at conventional frequencies.