A novel sandwich Ni-added polyoxometalate with nonlinear optical properties and photothermal conversion performance

Abstract

An acentric sandwich-type Ni-added polyoxometalate (NiAP), (NH₄)Cs_7.5Na_0.5H₂[Ni(H₂O)₃Ni₃(H₂O)(PW₈O₃₁)(PW₉O₃₄)]Cl·9H₂O (1), was synthesized using lacunary directing synthesis. Single crystal X-ray diffraction analysis revealed that 1 features a central Ni₃O₄ cluster sandwiched between PW₈O₃₁ and PW₉O₃₄. Nonlinear optical tests revealed that 1 exhibited a second harmonic generation response approximately 0.8 times that of potassium dihydrogen phosphate. The introduction of nickel ions with absorption in the near-infrared region significantly improved the photothermal conversion efficiency. Under 808 nm laser irradiation, the temperature of 1 increased by 70 °C within 90 seconds. A photothermal conversion efficiency of 20.5% was achieved. This approach offers a novel perspective on photothermal conversion.