Effect of cerium oxide addition on the optical absorption edge of tungsten trioxide

• Published in: Journal of materials science 1993, Vol.28 (1), p.239-242
• Main Authors: YAGOUBI, B, HOGARTH, C. A
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/BF00349056

Thin films of WO sub(3)/CeO sub(2) deposited by vacuum co-evaporation (10 super(-6) torr) on the Corning 7059 glass slides at room temperature have been shown to be amorphous in structure. The optical absorption spectra of amorphous WO sub(3)/CeO sub(2) thin films have been measured at room temperature. The optical absorption edge of WO sub(3)/CeO sub(2) and WO sub(3) thin films above 10 super(5) cm super(-1) follows the Davis and Mott equation for the non-direct optical transitions. The optical absorption coefficient, alpha , below this obeys the Urbach exponential relation. The value of the optical band gap of amorphous WO sub(3) thin films is in good agreement with that found by Deb. The shift of the optical gap to lower energies and that of the Urbach energies to higher energies as the content of CeO sub(2) is increased, indicate that both parameters are strongly dependent on the concentration of Ce super(4+) present in the structure. Thus, the increase of Ce super(4+) is thought to lead to strong potential fluctuations which cause an increase in the density of localized states in the gap.