K2Au(IO3)(5) and beta-KAu(IO3)(4): Polar Materials with Strong SHG Responses Originating from Synergistic Effect of AuO4 and IO3 Units

摘要

Two new polar potassium gold iodates, namely, K2Au(IO3)(5) (Cmc2(1)) and beta-KAu(IO3)(4) (C2), have been synthesized and structurally characterized. Both compounds feature zero-dimensional polar [Au(IO3)(4)] (-) units composed of an AuO4 square-planar unit coordinated by four IO3- ions in a monodentate fashion. In beta-KAu(IO3)(4), isolated [Au(IO3)(4)](-) ions are separated by K+ ions, whereas in K2Au(IO3)(5), isolated [Au(IO3)(4)](-) ions and non-coordinated IO3- units are separated by K+ ions. Both compounds are thermally stable up to 400 degrees C and exhibit high transmittance in the NIR region (lambda = 800-2500 nm) with measured optical band gaps of 2.65 eV for K2Au(IO3)(5) and 2.75 eV for beta-KAu(IO3)(4). Powder second-harmonic generation measurements by using lambda = 2.05 mm laser radiation indicate that K2Au(IO3)(5) and beta-KAu(IO3)(4) are both phase-matchable materials with strong SHG responses of approximately 1.0 and 1.3 times that of KTiOPO4, respectively. Theoretical calculations based on DFT methods confirm that such strong SHG responses originate from a synergistic effect of the AuO4 and IO3 units.