Crystal field and hyperfine structure of Er3+167 in YPO4 :Er single crystals: …

We report on a high-resolution optical and magneto-optical spectroscopy, luminescence, and electron paramagnetic resonance (EPR) studies of yttrium orthophosphate single crystals doped with erbium, which are promising telecom-wavelength materials for applications in quantum electronics and quantum information processing. An observation of the hyperfine structure in optical spectra of $^{167}\mathrm{Er}$ isotope in ${\mathrm{Er}:\mathrm{YPO}}_{4}$ is presented. Energies and symmetries of 40 crystal-field levels of ${\mathrm{Er}}^{3+}$ in ${\mathrm{Er}:\mathrm{YPO}}_{4}$ and $g$ factors of some of them were determined and successfully modeled on the basis of crystal-field calculations. The obtained set of crystal-field parameters was used in modeling the hyperfine structure observed in the optical and EPR spectra of ${\mathrm{Er}:\mathrm{YPO}}_{4}$ single crystals.