Experimental study of CdCl_2:CuCl photochromic coatings

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.