Polar Bismuth Selenite Iodate Oxide BiSeIO₆ with Three Types of Lone Pair Cations in One Structure

Abstract

Novel bismuth selenite iodate oxide BiSeIO 6 was synthesized in a mild hydrothermal condition. BiSeIO 6 was crystallized in the polar space group Pna2 1 of an orthorhombic system. The crystal structure features a three-dimensional framework composed of three types of lone pair cations with distorted BiO 7 polyhedra, SeO 3 pyramids, and IO 3 pyramids in one structure. Interestingly, BiSeIO 6 exhibits a strong and phase-matchable second-harmonic generation (SHG) of ∼6 times that of KH 2 PO 4 (KDP). Dipole moment analysis shows that all three local acentric groups of BiO 7 , SeO 3 , and IO 3 cooperatively contribute to the large macroscopic polarization and thereby strong SHG efficiency of BiSeIO 6 . In addition, BiSeIO 6 has a broad transparency range from 0.35 to 11 μm, indicating its promising nonlinear optical applications from visible to mid-infrared bands.

Analogous Chain Selenite Chlorides Ba2M(SeO3)2Cl2 (M = Cu2+, Ni2+, Co2+, Mn2+) and Pb2Cu(SeO3)2Cl2 with Tunable Spin S: Syntheses and Characterizations

“…The spectra suggest that the optical band gaps of 1 – 5 are 3.20, 4.85, 4.74, 4.56, and 2.90 eV, respectively. The compounds of 2 , 3 , and 4 are wide band gap semiconductors, larger than 3.50 eV for BiSeIO 6 , 3.30 eV for Na 3 Ti 3 O 3 (SeO 3 ) 4 F, 3.80 eV for Bi 3 (SeO 3 ) 3 (Se 2 O 5 )­F, 3.75 and 3.45 eV for PbBi­(SeO 3 ) 2 F and Pb 2 Bi­(SeO 3 ) 2 Cl 3 , 3.26 eV for Pb 2 TiFO­(SeO 3 ) 2 Br, but smaller than 5.62 and 5.77 eV for K­(GaF 2 ) 3 (SeO 3 ) 2 and NH 4 (GaF 2 ) 3 (SeO 3 ) 2 . The band gaps of compounds 1 and 5 are smaller than those above but larger than 2.35 eV for Pb 2 (V 2 O 4 F)­(VO 2 )­(SeO 3 ) 3 , 2.83 and 2.15 eV for Fe 2 O­(SeO 3 ) 2 and Fe 2 (SeO 3 ) 3 ·3H 2 O .…”