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.