Pb2Ga3F6(SeO3)2X3·2H2O (X = Cl, Br): two new HTO-type members exhibiting large NLO effects mediated by ionic mixing and substitution strategies

Abstract

The anion mixing strategy and equivalent substitution of functional groups are two effective and controllable methods to improve the probability of obtaining noncentrosymmetric (NCS) structures and optimizing nonlinear optical (NLO) performance. Herein, Pb₂Ga₃F₆(SeO₃)₂X₃·2H₂O (X = Cl and Br) are discovered via cation group substitution and introduction of oxyfluoride [GaF₄O₂] octahedra. They are also the first examples possessing two kinds of halogen atoms in the hexagonal tungsten oxide (HTO) family. Pb₂Ga₃F₆(SeO₃)₂Cl₃·2H₂O and Pb₂Ga₃F₆(SeO₃)₂Br₃·2H₂O are isostructural and crystalize in the noncentrosymmetric trigonal space group R32, and they feature a three dimensional (3D) framework with HTO-type [Ga₃F₆(SeO₃)₂]_∞ layers linked by [Pb₂Br₃]_∞ layers. Owing to the effective arrangement of chemical functional units, Pb₂Ga₃F₆(SeO₃)₂X₃·2H₂O exhibit strong SHG responses of 4.0–4.5 × KH₂PO₄ (KDP) and short UV cut-off edges of <300 nm, which are two essential parameters for NLO practical applications. The other physical and chemical properties of title compounds were evaluated in this work using IR spectroscopy, thermal parameter measurements, and theoretical calculations.