Cd₂ Nb₂ Te₄ O₁₅ : A Novel Pseudo-Aurivillius-Type Tellurite with Unprecedented Nonlinear Optical Properties and...

Oxides are emerging candidates for mid-infrared (mid-IR) nonlinear optical (NLO) materials. However, their intrinsically weak second harmonic generation (SHG) effects hinder their further development. A major design challenge is to increase the nonlinear coefficient while maintaining the broad mid-IR transmission and high laser-induced damage threshold (LIDT) of the oxides. In this study, it is reported on a polar NLO tellurite, Cd₂ Nb₂ Te₄ O₁₅ (CNTO), featuring a pseudo-Aurivillius-type perovskite layered structure composed of three types of NLO active groups, including CdO₆ octahedra, NbO₆ octahedra, and TeO₄ seesaws. The uniform orientation of the distorted units induces a giant SHG response that is ≈31 times larger than that of KH₂ PO₄ , the largest value among all reported metal tellurites. Additionally, CNTO exhibits a large band gap (3.75 eV), a wide optical transparency window (0.33-14.5 µm), superior birefringence (0.12@ 546 nm), high LIDT (23 × AgGaS₂ ), and strong acid and alkali resistance, indicating its potential as a promising mid-IR NLO material.