Chiral Polar Eu 2 (SeO 3 ) 2 (SO 4 )(H 2 O) 2 : A Pathway Toward Narrow Optical Line Widths and Microsecond Lifetimes for Quantum Memory Candidates

Stoichiometric materials of Eu(III) offer a promising platform for quantum memories attributable to their unique capability to display a distinctive, nondegenerate 5 D 0 → 7 F 0 transition, which enables precise mapping of optical quantum states into their energy-level manifold─a prerequisite for reliable storage and retrieval on demand. However, placing Eu(III) into chiral polar structures, which are necessary for achieving narrow spectral line widths and long optical lifetimes, is a daunting task. Here, we discover Eu 2 (SeO 3 ) 2 (SO 4 )(H 2 O) 2, a rare Eu(III) material that exhibits chiral polar symmetries encompassing both local and global structures. This unique structure is shaped by an appropriate combination of asymmetric ligands. Chirality fosters dipole–dipole interactions and J -mixing, as evidenced by second-harmonic generation, photoluminescence, and magnetic susceptibility. The broken inversion symmetry is supported by the phase-matching behavior in second-harmonic generation. The 5 D 0 → 7 F 0 transition is observed at 578 nm (2.145 eV) with 7.42 meV line width and 3.39 μs lifetime at T = 78 K. The analysis of magnetic susceptibility data using Van Vleck’s theory results in an effective magnetic moment of ρ eff = 3.33 μ B /Eu 3+ and J -mixing. Heat capacity data reveal underlying phonon dynamics in the material. This study demonstrates a pathway to realizing new chiral stoichiometric Eu 3+ compounds with potential for optically addressable quantum memory applications.