Molecular Engineering toward an Enlarged Optical Band Gap in a Bismuth Sulfate via Homovalent Cation Substitution

Materials capable of generating coherent short-wave (<300 nm) light have attracted extensive scientific and technical interest due to their wide utilization in laser research. In this study, a the rare-earth-metal sulfate NaCe(SO4)2(H2O) (NCSO) was synthesized through a hydrothermal method, while NaBi(SO4)2(H2O) (NBSO) was successfully obtained via a homovalent cation substitution of the parent compound NCSO under hydrothermal conditions. The space groups of crystalline NCSO and NBSO are P3121 and P3221, respectively. Both compounds have similar connectivities which feature a three-dimensional channel structure formed by asymmetric [CeO9]15-/[BiO9]15- tricapped trigonal prisms and distorted [SO4]2- tetrahedra. The introduction of Bi3+ with larger ionic radii and stereochemically active lone-pair electrons simultaneously enhanced the SHG effect and band gap of NBSO in comparison to its parent compound NCSO. In contrast to NCSO, which possesses a narrow energy band gap (2.46 eV), NBSO displays the largest energy band gap (4.54 eV) among the reported bismuth sulfate NLO materials. Powder frequency-doubling-effect measurements exhibit that NCSO and NBSO possess phase-matchable SHG responses of 0.2 × KDP and 0.38 × KDP at 1064 nm, respectively. Theoretical studies have been implemented to further elucidate the structure-performance relationships of the two compounds. Experimental and theoretical studies both demonstrate that NBSO may be a promising nonlinear material applied in the short-wavelength region.