Band gap modulation and nonlinear optical properties of quaternary tellurates Li 2 GeTeO 6 .

Tellurate crystals are attractive for developing new nonlinear optical (NLO) materials in the mid-infrared region due to their wide transmission window. In this work, we report a quaternary tellurate oxide crystal, Li ₂ GeTeO ₆ , which exhibits a short cutoff edge (240 nm) with a powder second harmonic generation (SHG) response of 1.3 × KH ₂ PO ₄ (KDP). The reported material reveals the largest band gap in the Li ₂ MTeO ₆ (M = tetravalent cation) family. The first-principles calculations were used to illustrate the origin of the NLO effect. These results highlight the band gap engineering based on the cation substitution strategy for designing new NLO materials with balanced optical properties.