Rational Design of a Niobium Tellurite Crystal Nb₂Te₃O₁₁ Exhibiting Good Overall Infrared NLO Performance by...

Nonlinear optical (NLO) materials have aroused increasing interest owing to their promising applications in optoelectronic technologies. Herein, we present the synthesis of an acentric niobium tellurite crystal, Nb₂Te₃O₁₁, extracted via a spontaneous crystallization approach. It adopts a unique three-dimensional (3D) structure constructed by the distorted [TeO₃], [TeO₄], and [NbO₆] fundamental building units. The title compound undergoes incongruent melting at approximately 807 °C. Optical characterizations demonstrate that Nb₂Te₃O₁₁ possesses an extended transparency window beyond 5 μm, along with a large band gap value of 3.1 eV. Moreover, the as-synthesized Nb₂Te₃O₁₁ displays an appreciable second-harmonic generation (SHG) response of 2 × KDP and a notable birefringence of 0.11 under 1064 nm for achieving phase-matching. In addition, theoretical calculation investigations suggest that the intriguing optical properties are ascribed to the cooperative effect of three types of NLO-active motifs: [TeO₃] pyramids, [TeO₄] seesaws, and [NbO₆] octahedra. These attributes provide new functional insights into Nb₂Te₃O₁₁ and enrich the family of NLO crystals in the mid-infrared region.