Li 13 YGe 4 O 16 : A Mid-infrared Rare-Earth Germanate Nonlinear Optical Crystal Featuring a Broad Transmission Range and an Enlarged Band Gap.

Germanate is garnering increasing attention in the field of optoelectronics owing to its competitive optical transparency and robust stability. Herein, a novel lithium-rich rare-earth germanate, Li 13 YGe 4 O 16 , was fabricated for the first time using a high-temperature solution approach. This compound adopts the asymmetric space group Cmc 2 1 (no. 36), characterized by isolated [YO 6 ] and [GeO 4 ] structural motifs with Li + cations located in the channel. Notably, Li 13 YGe 4 O 16 presents a short ultraviolet cutoff edge at 240 nm, indicative of an enlarged band gap of 4.96 eV and showcases a wide mid-infrared transmission region exceeding 6.0 μm. Moreover, Li 13 YGe 4 O 16 features exceptional thermal stability and moderate second harmonic generation (SHG) intensity. Additionally, a theoretical analysis suggests that the distorted [YO 6 ] octahedra. [GeO 4 ] and [LiO 4 ] tetrahedra play a significant role in the optical activities of Li 13 YGe 4 O 16 . These attributes endow Li 13 YGe 4 O 16 with the potential to serve as a new mid-IR nonlinear optical (NLO) crystal and enrich the structural chemistry of germanates.