Metal Chloride-Iodate Nonlinear Optical Materials via Direct Chlorination of Centrosymmetric Metal Iodate Crystals

Noncentrosymmetric (NCS) crystals may show many interesting and important physical properties and wide applications in science and technology but they are rare in contrast to centrosymmetric crystals. The development of NCS crystals from known centrosymmetric (CS) crystals is of fundamental and applied importance. Herein, a simple and effective strategy that by addition of appropriate diluted HCl into CS crystals to react directly was proposed for the reversal of the CS to NCS structure by utilizing the structural directing agents Cl^- anion to break the symmetry and then to regulate orientation and arrangement of anionic moieties. The resultant a family of NCS iodates AM(IO₃)₃Cl (A = Rb, Cs; M = Al, Ga, Fe) were successfully developed via Cl^- anion- induced transformation from parent CS A₂M(IO₃)₄(H_0.5IO₃)₂ and Cs₂Fe(HIO₃)(IO₃)₅. Remarkably, Al- and Ga-based compounds RbAl(IO₃)₃Cl, CsAl(IO₃)₃Cl, and CsGa(IO₃)₃Cl exhibit the strong second harmonic generation (SHG) responses (11.0-12.5 × KDP), large band-gaps (4.00-4.17 eV), high laser damage thresholds (LDTs), wide transparent wavelength regions, and easiness of growing up large crystal. This work provides a new perspective to develop important NCS crystals from CS crystals.