HBa(IO)(IO) and HBa(IO)(IO): Explorations of Second-Order Nonlinear Optical Materials in the Alkali-Earth Polyiodate System.

Two new barium polyiodate compounds in the alkali-earth system, namely, HBa(IO)(IO) ( Fdd2) and HBa(IO)(IO) ( P1̅) have been obtained through hydrothermal reaction. Interestingly, the structures of both compounds feature different polyiodate groups, i.e., IO and IO groups. HBa(IO)(IO) can be depicted as an alternative stacking of two-dimensional (2D) [Ba(IO)(IO)] and [Ba(IO)(IO)] layers with the IO and IO group serving as linkers. HBa(IO)(IO) can be depicted as a 3D network with 2D [Ba(IO)] layers being interconnected by IO groups. The 0D IO polyiodate group can be seen also viewed as formed by an IO group further corner-sharing with an IO group or an IO group further corner-sharing with two IO groups. Powder second harmonic generation (SHG) measurements show that HBa(IO)(IO) crystals display a moderate SHG efficiency of ∼1.6 times that of KHPO (KDP) and are phase-matchable. Optical properties measurements, thermal analyses, and laser damage threshold (LDT) measurements have been performed. Results of theoretical calculation show that the formation of IO is thermodynamically much easier than IO and IO, because of the lower reaction energy. Our studies shed light on exploring alkali-earth polyiodates as potential NLO materials.