Balanced IR Nonlinear Optical Performance Achieved by Cation–Anion Module Cosubstitution in V-Based Salt-Inclusion Oxychalcogenides

Oxychalcogenides have become notable contenders for infrared nonlinear optical (IR NLO) applications because of their diverse heteroanionic functional motifs. However, while the main group elements are well-explored for these motifs, transition elements have been less studied and lack high-performance materials. To address this gap, we investigated a series of noncentrosymmetric [Ba4(Ba6S)][(VOxS4–x)6] (space group: P63), the first V-based salt-inclusion oxychalcogenides demonstrating phase-matched IR-NLO properties. We achieved this by cation–anion module cosubstitution in the centrosymmetric structure of [Ba4(Ba6Cl2)][(VO4)6] (space group: P63/m). The novel [Ba4(Ba6S)][(VOxS4–x)6] features isolated heteroanionic [VOxS4–x]3– units, charge-balanced Ba2+ cations, and a one-dimensional cationic chain of [Ba6S]10+ octahedral units. Moreover, [Ba4(Ba6S)][(VO3S)6] exhibits notable properties including a high second-harmonic-generation intensity (1.33 × AgGaS2@2900 nm), a substantial laser-induced damage threshold (7.65 × AgGaS2), a broad IR cutoff edge (up to 11.2 μm), and significant birefringence for phase matching (Δn = 0.073@2900 nm). Structural analysis and DFT calculations demonstrate that the configuration of the [VO3S]3– units enhances NLO properties and increases structural anisotropy. Our findings suggest that V-based salt-inclusion oxychalcogenides are a promising class for IR-NLO applications and highlight cation–anion module cosubstitution as an effective approach for creating high-performance heteroanionic NLO crystals.