Photothermal Conversion of W₁₈O₄₉ with a Tunable Oxidation State

W₁₈O₄₉ with a tunable oxidation state was prepared by addition of NaNO₃ or NaBH₄ as a redox agent in the solvothermal system. The addition of redox agents has no influence on the crystallization of W₁₈O₄₉. The obtained W₁₈O₄₉ structures keep their morphology as a bundle of nanowires with a regular hexagonal on the cross-section. W₁₈O₄₉ exhibits strong valence-dependent absorption features in the near-IR region. Reduced W₁₈O₄₉ with more W⁵⁺ has a higher concentration of oxygen vacancies, which enhances the localized surface plasmon resonance effect. Reduced W₁₈O₄₉ exhibits a high photothermal conversion efficiency of 59.6 % and has good photothermal stability.