Unveiling the Intrinsic Superior SHG Performance of Ce⁴⁺ Fluoride Masked by Subtle Ce³⁺ Impurity and Its Effective Removal

Abstract Owing to its unique electronic configuration [Xe]4 f 0 , Ce 4+ ‐compound is a highly desired in the field of advanced nonlinear optical materials, yet its synthesis remains a great challange. Herein, we report a series of cerium fluorides, including a pure Ce 4+ ‐fluoride, high‐performance Na 2 (Ce 4+ )F 6 ; three mixed valance state samples, (Mix1–3, with increasing Ce 3+ concentration); and a fully reduced pure Ce 3+ ‐fluoride Na 1.5 (Ce 3+ ) 1.5 F 6 . In particular, Na 2 (Ce 4+ )F 6 , shows an SHG response (4×KDP), and a wide band gap (4.77 eV), which are the strongest and widest among all Ce‐containing materials to date. With systematic studies, we demonstrate that the subtle Ce 3+ impurity significantly reduces performance. By being aware of this fact and consciously controlling experimental conditions, we can ensure the synthesis of pure Na 2 (Ce 4+ )F 6 , which exhibits excellent overall performance and shows great potential for future applications. This work not only reinforced the crucial role of Ce 4+ in significantly enhancing the key performance, but also provided invaluable experimental evidence and theoretical support for the future design of more efficient and superior functional materials.