Abstract

We present measurements of the spectral transmittance and photochromic response of CdCl₂:CuCl coatings. The coatings are also examined with the aid of electron micrographs. We explain the features observed in the spectral transmittance of darkened photochromic films, using a colloidal model obtained from the generalized Maxwell-Garnett theory. The colloidal model indicates the presence of ellipsoidal copper particles with a shape factor (minor axis/major axis) between 0.39 and 0.42 and mean ratios between 2.03 and 1.73 nm. The optical transmittance curve obtained in the faded state shows a peak near 280 nm attributed to Cu⁺, and the curve in the darkened state shows two bands, a band located at 375 nm attributed to Cu²⁺ and another at 600–610 nm assigned to colloidal copper particles.

© 1990 Optical Society of America

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