Lei Geng

BaBi(SeO3)2Cl: a new polar material showing high second-harmonic generation efficiency enhanced by constructive alignment of chloride ions

The novel oxychloride BaBi(SeO3)2Cl with polar crystal structure was first synthesized by using hydrothermal method at a mild temperature of 200 °C. It crystallizes in the orthorhombic Cmc21 (36) space group with cell parameters of a = 5.2804(2) A, b = 20.0535(9) A, c = 6.9070(3) A, V = 731.39(5) A3, and Z = 4. The compound features a two-dimensional [Bi(SeO3)2Cl]2− anionic layer structure stacking along the crystallographic b-axis direction. Within the [Bi(SeO3)2Cl]2− layer, BiO4 quadrangular pyramids bridge two types of Se(1)O3 and Se(2)O3 triangular pyramid through corner-sharing manner into a [Bi(SeO3)2]− chain. The [Bi(SeO3)2]− chains are aligned along c-axis direction with chloride ions adjacent to bismuth cations, and the 2D [Bi(SeO3)2Cl]2− forms. As a consequence, local dipole moments of the building block layers are arranged in a constructive fashion, which is favourable to enhance the second-order nonlinear properties of materials. Powder Kurtz–Perry method was utilized to evaluate the second-harmonic generation (SHG) efficiency, indicating a strong SHG effect (about 16 times that of KH2PO4 (KDP) reference). More excitingly, BaBi(SeO3)2Cl can achieve type I phase-matching, which make the compound feasible for practical applications. In addition, first-principles density functional theory (DFT) calculations were also performed to illustrate the relationships between crystal structure and optical properties.

Syntheses and Properties of Some Bi-Containing Compounds with Noncentrosymmetric Structure

A genetic engineering method is employed to design the second harmonic generation (SHG) materials with infrared transparency. The compounds of Ba2BiInA5 (A = S, Se, Te) are constructed in views of “genome” BiA5 pyramid and InA4 tetrahedron. Then, the crystal structures of these compounds are predicted or reproduced to show their non-centrosymmetry based on global optimization evolutionary methodology. Thirdly, the ab initio computations of band structures and simulations of optical properties are carried, and the nonlinear optical figure of merit in views of optical transparent range and the SHG parameters are surveyed for these crystals. Finally, we provide the substance evidences by the experimental synthesis, crystal structural determinations, and optical measurements for Ba2BiInA5 (A = S, Se) compounds.