Characterization of the hyperfine interaction in europium-doped yttrium orthosilicate and europium chloride hexahydrate

We present characterization of the hyperfine interaction for the europium in hydrated europium chloride and as a dopant in yttrium orthosilicate. The Zeeman and pseudoquadrupole tensors were determined by measuring the hyperfine splittings while rotating the direction of a weak (similar to 300 G) magnetic field. The hyperfine spectra were recorded using Raman-heterodyne spectroscopy, an radio-frequency optical double resonance technique. For both materials magnetic field values were identified where there is no first order Zeeman shift in a europium hyperfine transition. These field insensitive transitions will have application in achieving very long hyperfine coherence times.