Ytterbium-ion pairs in Yb:CsCdBr₃; ion-ion interaction and the electronic ground state investigated by electron paramagnetic resonance spectroscopy

Abstract

Electron paramagnetic resonance spectra of Yb3+ ions in the optically bistable compound Yb:CsCdBr3 are presented. The features observed are assigned to the symmetrically coupled pair complexes of the type Yb3+-VCd-Yb3+ (VCd being a cadmium vacancy) whose axis is parallel to the crystallographic c-axis. There are no asymmetric pairs of the type Yb3+-Yb3+-VCd. It is shown that simulation of the spectra is possible only if an exchange interaction is taken into account in the spin Hamiltonian. The value of J = -0.0016 cm-1 shows that the exchange interaction is antiferromagnetic but extremely weak. It is also found that there is a significant relaxation (about 12%) of Yb3+ ions toward the Cd vacancy. From the experimental g-tensor values, it is established that the lower ground state of Yb3+ ions in CsCdBr3 is mainly composed of 4fϕ (63%) and 4fδ (32%) ytterbium orbitals. It has been previously proposed that optical bistability is due to asymmetric pairs of the type Yb3+-Yb3+-VCd. On the basis of the present work, this now appears unlikely.