Chiral Polar Eu₂(SeO₃)₂(SO₄)(H₂O)₂: A Pathway Toward Narrow Optical Line Widths and Microsecond Lifetimes for Quantum...

Stoichiometric materials of Eu(III) offer a promising platform for quantum memories attributable to their unique capability to display a distinctive, nondegenerate ⁵D₀ → ⁷F₀ 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 Eu₂(SeO₃)₂(SO₄)(H₂O)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 ⁵D₀ → ⁷F₀ 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/Eu³⁺ and J-mixing. Heat capacity data reveal underlying phonon dynamics in the material. This study demonstrates a pathway to realizing new chiral stoichiometric Eu³⁺ compounds with potential for optically addressable quantum memory applications.