Metal iodates have long been the research focus because they are valuable candidates as second harmonic generation (SHG) materials. It has been reported that the condensation of iodate units into polyiodate as SHG-active group is an effective approach for exploring novel SHG materials.  

In a study published in Angewandte Chemie, a research group led by Prof. MAO Jianggao from the Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences proposed that REI₅O₁₄ (RE = Y and Gd) were promising SHG materials featuring semi-circle shaped I₅O₁₄^3- polyiodate anion. They were obtained via the hydrothermal reactions of RE₂O₃ and H₅IO₆ in H₃PO₄ (≥85 wt. % in H₂O).   

Researchers found that each brand-new I₅O₁₄ pentamer was composed of three IO₄ and two IO₃ units via corner-sharing was arranged properly, resulting in very strong SHG response (14 × and 15 × KH₂PO₄(KDP) for Y and Gd compounds).   

Theoretical calculations showed that I₅O₁₄ pentamer were the mainly SHG-contributed amount (91.28% for YI₅O₁₄ and 92.62% for GdI₅O₁₄). Meanwhile, REI₅O₁₄ (RE = Y and Gd) were widely transparent from visible to mid-infrared spectral region.  

They revealed that hydrothermal reaction under phosphoric acid medium facilitated the formation of polyiodate anion, probably because the fact that the consistency of reaction media was strengthened by H₃PO₄.   

This study provides a facile and effective approach for exploring new SHG materials based on metal iodates.  

I₅O₁₄ pentamer and oscilloscope traces of the SHG signals (Image by Prof. MAO’s group)