A Polar Cerium Iodate Ce ₂ (IO ₃ ) ₆ (H ₂ O) with a Strong Second-Harmonic Generation Response in Trivalent Ce-Based Materials

Ce-based polar materials are promising NLO candidates due to their unique electronic configuration of [Xe] 4f¹5d¹6s² and diverse coordination modes. Ce⁴⁺ compounds are highly desired candidates for advanced nonlinear optical materials, yet the development of trivalent cerium-based NLO materials exhibiting a high second-harmonic-generation (SHG) response (above 3.0 × KDP) remains a great challenge. Herein, a new cerium iodate, Ce₂(IO₃)₆(H₂O), crystallized in the polar space group Pn (No. 7), was discovered by introducing rare-earth cations into iodates with a hydrothermal method, where corner-shared distorted [CeO₉] polyhedra and [IO₃]⁻ groups alternately connect to assemble a three-dimensional (3D) framework. Optical studies showed that Ce₂(IO₃)₆(H₂O) exhibits strong SHG intensities (3 × KDP), a large band gap of 2.83 eV in the trivalent Ce-based NLO materials, indicating its potential application in frequency conversion. First-principles simulations of Ce₂(IO₃)₆(H₂O) were conducted to investigate the molecular structure and optical properties. First-principles calculations, informed by structural analysis, indicate that the two kinds of polarizable cerium-centered polyhedra ([Ce(1)O₉] and [Ce(2)O₈(H₂O)]) constitute the primary contribution to the SHG coefficients.