Optical Absorption of Transition Element Oxide-Silica Coating Films Prepared by Sol-Gel Method

Abstract

The valence and coordination of the transition element in the transition element oxide-silica coating films prepared by sol-gel method were examined by measuring the optical absorption spectra and compared with those found in the silica glass containing a transition element oxide prepared by Schultz by flame-hydrolysis at high temperatures. The following results were obtained:
(1) The maximum possible content of a transition element oxide for obtaining homogeneous film was 10mol% for Cr₂O₃, 20mol% for Mn₂O₃, 45mol% for Fe₂O₃, 45mol% for CoO, 55mol% for NiO and 45mol% for CuO. The optical transmittance at 555nm of the homogeneously colored 0.2-0.5μm thick films with strongest absorption was 81% for Cr, 68% for Mn, 63% for Fe, almost 0% for Co, 59% for Ni and 95% for Cu.
(2) The valence and coordination of a transition element in the films were similar to those found in silica glass prepared at high temperatures. However, the concentration of a transition element showing a certain valence and coordination was not equal to that found in silica glass prepared at high temperatures. It was found that chromium is present as Cr³⁺ in octahedral site, manganese as Mn³⁺ in octahedral site, iron as Fe³⁺ in octahedral site, cobalt as Co²⁺ in tetrahedral site, nickel as Ni²⁺ in octahedral site and copper as Cu²⁺ in octahedral site.