Halogen-Driven Structural Engineering in Tellurium Oxyhalides: Enhanced SHG Response and Broad Optical Transparency

Oxyhalides are promising candidates for nonlinear optical (NLO) applications due to their unique structural and optical properties. In this study, we report the synthesis of two tellurium-based oxyhalides, Te₈O₁₅Cl₂ and Te₆O₁₁Cl₂, which exhibit distinct structural features and exceptional optical performance. Te₈O₁₅Cl₂ crystallizes in a noncentrosymmetric 2D layered structure, while Te₆O₁₁Cl₂ adopts a centrosymmetric 1D chain arrangement. Both compounds display wide optical transmission windows (0.30/0.31–25 μm), with Te₈O₁₅Cl₂ achieving a large second-harmonic generation (SHG) efficiency surpassing conventional materials and a significant birefringence (Δn = 0.185 at 546 nm). The SHG response of Te₈O₁₅Cl₂ is attributed to the alignment of nonlinear-active units driven by the [TeO₃Cl] disphenoid and the stereochemically active lone pairs (SCALPs), facilitated by halogen-mediated structural distortion. These results highlight the potential of halogen modification for the design of advanced NLO materials with enhanced performance.