Crystalline Mixed Halide Halobismuthates and Their Induced Second Harmonic Generation

Mixed
halide coordination has been widely used to finely tune the properties
of inorganic and inorganic–organic hybrid compounds, especially
for emerging perovskites materials. Despite the increasing number
of reports on preparation methods and the affected functionalities,
the peculiar and precise role of the doping halogens in structural
regulation of the crystals and the resulting variations on the basic
properties remain to be addressed. Here, to shed light into the “black
box”, a new series of [NH2(CH2CH3)2]3Bi­(Cl1–xBrx)6 (x = 0, 0.135, 0.255, 0.385, 0.847, and 1) single crystals were grown
from the mixed halide solvents by the temperature lowering method.
The correlation between the inclusion amounts of Br in the final crystals
with the halide concentrations in the precursors is discussed from
different perspectives. The two kinds of halogens share the same position
in the mixed halide system, with every crystallographically independent
halide site possessing different halogen occupancies. The mixed halide
coordination exhibits a regulated effect on the distortion of the
anion octahedra. Optical absorption, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), and the second harmonic generation
(SHG) measurements have confirmed that, with increased Br inclusion,
[NH2(CH2CH3)2]3Bi­(Cl1–xBrx)6 crystals exhibit a regulated effect on their
bandgaps, thermal stabilities, and SHG capacities.