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

Abstract

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 [Ba 4 (Ba 6 S)][(VO x S 4−x ) 6 ] (space group: P6 3 ), 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 [Ba 4 (Ba 6 Cl 2 )][(VO 4 ) 6 ] (space group: P6 3 /m). The novel [Ba 4 (Ba 6 S)][(VO x S 4−x ) 6 ] features isolated heteroanionic [VO x S 4−x ] 3− units, charge-balanced Ba 2+ cations, and a one-dimensional cationic chain of [Ba 6 S] 10+ octahedral units. Moreover, [Ba 4 (Ba 6 S)][(VO 3 S) 6 ] exhibits notable properties including a high second-harmonic-generation intensity (1.33 × AgGaS 2 @2900 nm), a substantial laser-induced damage threshold (7.65 × AgGaS 2 ), 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 [VO 3 S] 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.