Synthesis, crystal and electronic structures, linear and nonlinear optical properties, and photocurrent response of oxyhalides CeHaVIO4 (Ha = Cl, Br; VI = Mo, W)

Abstract

Four heteroanionic oxyhalides, CeClMoO₄, CeBrMoO₄, CeClWO₄, and CeBrWO₄, have been studied as multifunctional materials, which show a combination of good second harmonic generation (SHG) response and photocurrent signals. Millimeter-sized CeHaVIO₄ (Ha = Cl, Br; VI = Mo, W) crystals were grown by halide salt flux. The crystal structure of CeHaVIO₄ crystals was accurately determined by single-crystal X-ray diffraction. CeClMoO₄, CeBrMoO₄, and CeBrWO₄ are isostructural to each other, and crystallize in the acentric LaBrMoO₄ structure type. CeClWO₄ crystallizes in a new structure type with unit cell parameters of a = 19.6059(2) Å, b = 5.89450(10) Å, c = 7.80090(10) Å, and β = 101.4746(8)°. The bandgaps of CeHaVIO₄ fall into the range of 2.8(1)–3.1(1) eV, which are much smaller than those of isotypic LaHaVIO₄ (Ha = Cl, Br; VI = Mo, W) in the range of 3.9(1)–4.3(1) eV. The narrowing of bandgaps in CeHaVIO₄ originates from the presence of partially filled 4f orbitals of cerium atoms, which was confirmed by density functional theory (DFT) calculations. The moderate bandgaps make CeHaVIO₄ suitable for infrared nonlinear optical (IR NLO) applications. CeBrMoO₄ and CeBrWO₄ exhibit moderate SHG responses of 0.58× AGS and 0.46× AGS, respectively, and are both type-I phase-matching materials. Moderate SHG response, easy growth of crystals, high ambient stability, and type-I phase-matching behavior make CeBrMoO₄ and CeBrWO₄ great materials for IR NLO applications. CeHaVIO₄ films also exhibited good photocurrent response upon light radiation. This work demonstrates the rich structural chemistry of the REHaVIO₄ (RE = Y, La–Lu; Ha = Cl, Br; VI = Mo, W) family and the potential presence of more multifunctional materials.