Explorations of New Second-Order Nonlinear Optical Materials in the KI-MII -IV-O Systems

Explorations of new second-order nonlinear optical (NLO) materials in the KI-MII -IV-O systems led to four novel mixed metal iodates, namely, K2M(IO3)4(H2O)2 (M = Mn, Co, Zn, Mg). The four compounds are isostructural and crystallize in space group I2 which is in the chiral and polar crystal class 2. Their structure features zero-dimensional {M(IO3)4(H2O)2}2− anions that are separated by K+ cations. The M(II) centers are ligated by two aqua ligands in trans fashion and four monodentate iodate anions. The K+ cation is eight-coordinated by two iodate anions in bidentate chelating fashion and four other iodates in a unidentate fashion. Second harmonic generation (SHG) measurements indicate that K2Zn(IO3)4(H2O)2 and K2Mg(IO3)4(H2O)2 display moderate SHG responses that are approximately 2.3 and 1.4 times of KH2PO4 (KDP), respectively, and they are also phase-matchable. The SHG response of K2Co(IO3)4(H2O)2 is much weaker (about 0.3×KDP), and no obvious SHG signal was detected for K2Mn(IO3)4(H2O)2. Results of optical property calculations for the Zn and Mg phases revealed SHG responses of approximately 5.3 and 4.7 times of KDP, respectively, the order of Zn > Mg is in good agreement with the experiment data.