Zeeman Effect, Polarization, and Selection Rules ofSm2+:K+Vacancy Pair Fluorescence in KCl

The fluorescence of ${\mathrm{Sm}}^{2+}$ ions in KCl has been studied at 4.2°K under a magnetic field of 26 kG. First-or second-order Zeeman effect has been observed in half of the observed emission lines. The anisotropy of the Zeeman effects has been observed in lines resulting from transitions between the ${}_{}{}^5{}_{}{}^{}D$ term and the ${}_{}{}^7{}_{}{}^{}F_4^{}{}_{}{}^{}$, ${}_{}{}^7{}_{}{}^{}F_5^{}{}_{}{}^{}$, and ${}_{}{}^7{}_{}{}^{}F_6^{}{}_{}{}^{}$ levels. On this basis, $C_{4v}$ sites arising from ${\mathrm{K}}^{+}$ vacancies oriented along the $〈100〉$ axes and $C_{2v}$ sites resulting from ${\mathrm{K}}^{+}$ vacancies oriented along the $〈110〉$ axes with respect to the ${\mathrm{Sm}}^{2+}$ ions have been positively identified. Polarization and selection rules of the ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}\to {}_{}{}^7{}_{}{}^{}F_J^{}{}_{}{}^{}$ transitions have been deduced for $C_{2v}$ and $C_{4v}$ site symmetries. An effective spin Hamiltonian with $S=1\mathrm{}$ has been employed to describe the Zeeman effect. The spin Hamiltonian for the identified $C_{2v}$ site symmetry, $H_{\mathrm{eff}}=g\beta \mathrm{H}·\mathrm{S}+D[{S_z}^2-\frac{1}{3}S(S+1\mathrm{}\left)\right]+E({S_{+}}^2+{S_{-}}^2),$ has a vanishing value for $E$ and resembles that for the $C_{4v}$ site symmetry. This is because the additional ligand field arising from the ${\mathrm{K}}^{+}$ vacancy is axial.