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Applied Optics

Applied Optics


  • Vol. 41, Iss. 31 — Nov. 1, 2002
  • pp: 6708–6724

Dopant-dependent reflectivity and refractive index of microcrystalline H x WO3 and Li x WO3 bronze thin films

Zahid Hussain  »View Author Affiliations

Applied Optics, Vol. 41, Issue 31, pp. 6708-6724 (2002)

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Reflectivity spectra of H x WO3 and Li x WO3 thin films were measured over the photon energy range from 0.4 to 4.2 eV. It was found that microcrystalline tungsten bronzes have reflectances of 8%–30% over the dopant concentration range x (0 ≤ x ≤ 0.25). Values for the real part of refractive index n were also determined from the refined reflectivity data. The optical data are interpreted by use of a modified Drude-Zener model together with a single-oscillator model to differentiate between bound and free electronic states. The values of high-frequency dielectric constant εhf of M x WO3 (M = H+, Li+) bronzes were determined from the refractive-index data for estimation of the effective electronic masses involved in optical and polaronic transitions. A single-oscillator model showed that oscillator energy E a and dispersion energy E d increased and decreased, respectively, with increasing x values, opposite what occurs in crystalline tungsten bronzes. These findings support the fact that Bloch electrons are almost absent; instead, the polaronic species (W5+ and W4+) are assumed to control the reflectivity modifications (or variations in the refractive index) that are associated with the microcrystalline tungsten bronzes.

© 2002 Optical Society of America

OCIS Codes
(120.4530) Instrumentation, measurement, and metrology : Optical constants
(160.2100) Materials : Electro-optical materials
(160.4760) Materials : Optical properties
(230.2090) Optical devices : Electro-optical devices
(240.0310) Optics at surfaces : Thin films
(310.6860) Thin films : Thin films, optical properties

Original Manuscript: March 29, 2002
Revised Manuscript: July 24, 2002
Published: November 1, 2002

Zahid Hussain, "Dopant-dependent reflectivity and refractive index of microcrystalline HxWO3 and LixWO3 bronze thin films," Appl. Opt. 41, 6708-6724 (2002)

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