Oxygen deficiencies and optical absorption in hexagonal tungsten bronze nanoparticles

Keisuke Machida; Mika Okada; Kenji Adachi

doi:10.1117/12.2319917

19 September 2018 Oxygen deficiencies and optical absorption in hexagonal tungsten bronze nanoparticles

Keisuke Machida, Mika Okada, Kenji Adachi

Proceedings Volume 10722, Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XVI; 1072223 (2018) https://doi.org/10.1117/12.2319917
Event: SPIE Nanoscience + Engineering, 2018, San Diego, California, United States

Abstract

Mechanism of low-energy optical absorptions in tungsten oxide and tungsten bronzes is still a matter of controversy, although plasmon and polaron mechanisms have been proposed as a dominant cause. In this report we studied Cs-doped hexagonal tungsten bronze (Cs-HTB) nanoparticles (NPs), known as a solar-control material, and show systematic analysis results on structural and optical changes with varied amount of oxygen vacancy (V_O) and alkali content. Chemical analysis of the Cs-HTB samples synthesized under a reducing gas flow revealed that their exact composition is described as Cs_xWO_3-y (y ≤ 0.46). With increasing Cs⁺ and V_O, lattice constants determined by XRD Rietveld method changed linearly and optical absorption peaks observed at 0.5-2.0 eV were found to intensify. The origin of the structural change is considered to be the destabilization of the pseudo Jahn-Teller distortion in WO₆ octahedra. The optical peaks were analyzed by the Drude-Lorentz analysis assuming coexisting anisotropic plasmon resonances and a polaron excitation, and by the Mie integration method to incorporate the ensemble inhomogeneity effect of NPs. This procedure enabled complete deconvolutions of the optical peaks, which indicated that the polaron absorption was caused by the localized electrons derived from V_O.

Citation Download Citation

Keisuke Machida, Mika Okada, and Kenji Adachi "Oxygen deficiencies and optical absorption in hexagonal tungsten bronze nanoparticles", Proc. SPIE 10722, Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XVI, 1072223 (19 September 2018); https://doi.org/10.1117/12.2319917

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