The sodium tungsten bronzes as plasmonic materials: fabrication, calculation and characterization

Abstract

The tungsten bronzes are non-stoichiometric transition metal oxides of the form MxWO3, where 0 ≤ x ≤ 1, and M is a dopant ion, most commonly an alkali metal. In this work, the sodium tungsten bronzes (NaxWO3) are investigated as materials for plasmonic applications. The bronzes were fabricated with a solid state reaction, the dielectric function calculated using density functional theory (DFT) and the nanoparticle responses calculated with the boundary element method (BEM). The results were compared to Au and Ag, the materials most widely used in plasmonic applications. It was shown that for x > 0.5, the solid state fabrication method produces cube-shaped particles of diameter ≥ 1 μm, whose bulk optical properties are well described by a free-electron model and a rigid band structure. The addition of Na into the lattice increases the free electron density, increasing the bulk plasma frequency. Nanoparticle plasmon resonances are found to be highly tunable, and generally at a lower frequency than Au or Ag, and so sodium tungsten bronzes are predicted to be well suited to biomedical or chemical sensing applications.

Plasmonic enhancement of aqueous processed organic photovoltaics

“… 47 The strong but narrow absorption peak at ∼230 nm in the ultraviolet (UV) range is attributed to the inter-band transition of Na x WO 3 plasmonic nanoparticle. 39 The transmission electron microscopy (TEM) image shown in Fig. 1b indicates that the size of nanoparticles is of the order of tens of nanometres.…”

“…[36][37][38] Recent work has assessed the feasibility of Na x WO 3 as an alternative plasmonic material since it exhibits strong plasmonic resonances compared to Au and offers simple nanofabrication at low cost. 39,40 In this work, plasmonic structured NP-OPV devices have been fabricated to study the light-matter interaction in the nanoscale region between metal oxide plasmonic nanoparticle and water processed photo-active layer. A combination of microscopic and lm physical/chemical spectroscopic techniques have been used to elucidate the multilayer lm morphology of Na x WO 3 NP-OPV devices and the effect of plasmonic nanoparticles on their performance.…”

Tunable Transparency and NIR-Shielding Properties of Nanocrystalline Sodium Tungsten Bronzes

“…This change in color can be attributed to increase of bulk plasma frequency ( ω p ) [ 6 ]. Unlike other metals, the ω p of Na x WO 3 can be tuned by Na content in WO 3 [ 11 , 12 ].…”

Morphological and chemical dynamics upon electrochemical cyclic sodiation of electrochromic tungsten oxide coatings extracted by in situ ellipsometry

“…Many studies focused on optical measurements and debated the coloration mechanism of sodium-tungsten bronzes. Thus, after pioneering works on optical properties [9], most reports on the dielectric functions were published in the 1970's and 1980's [10][11][12][13][14][15] whereas Tegg et al computed it recently by means of DFT [16]. The deep blue cathodic coloration in such EC system [17] arises from the cumulative generation of electronic transitions between different W n+ states, but based on different mechanisms in the amorphous or crystalline states [1] i.e.…”