Site‐Saturation Model for the Optical Efficiency of Tungsten Oxide‐Based Devices

Abstract

A site-saturation model for the variation in optical efficiency of tungsten oxide-based intercalation devices is presented. The model applies to situations in which a dominant fraction of the electrons associated with the intercalating species are appreciably localized. It is predicted that the optical efficiency diminishes with increasing intercalation level, reaching zero when half the sites are occupied. The model is quantitative and predictive. The model is compared to several sets of data which it matches well. The only parameters of the model are film thickness, maximum obtainable optical density, and relative density of the film. The range of suitability of the model and the interpretation of its comparison with experiment are discussed.

Optical absorption in lithiated tungsten oxide thin films: Experiment and theory

“…Our theory is a generalization of the site-saturation model of Denesuk and Uhlmann. 28 The original site-saturation model assumes that the optical absorption coefficient is proportional to the number of available electronic transitions from a W 5+ ion to a W 6+ one. Let p be the probability that an inserted electron becomes situated at a certain W 6+ site.…”

Polaron absorption in amorphous tungsten oxide films

“…At a high intercalation level, a saturation of the absorption occurs, as also predicted theoretically. 15 It should be noted that intercalated crystalline tungsten oxide exhibits strikingly different optical properties, like the alkali tungsten bronzes. 16 The optical spectra of these materials are dominated by free electron behavior for energies below the band gap, leading to a high metal-like reflectance at low energies.…”

Optical charge transfer absorption in proton injected tungsten oxide thin films analyzed with spectroscopic ellipsometry

“…5 shows the amplitude as a function of the concentration of intercalated protons, given by the x-values in H x WO 3 . The experimental results and theory are compared using the site-saturation model [16,18]. This model assumes that the optical absorption is proportional to the relative amount of available electronic transition between a W 6+ ion and a W 5+ one.…”