Tailoring the optical properties of metal-oxide electrochromic mixtures

A semi-empirical approach is given to show how an optical-shift parameter S (via the frequency maximum of an optical band) correlates with the composition of a mixture of electrochromic oxides such as tungsten trioxide, thereby allowing the colours of electrochromic oxide mixtures to be tailored. It is shown that changing the relative amounts of charge-donating oxygen-based moieties (oxide, pendant oxygen and bridging oxygen) in the mixture systematically varies the electrochromic colour according to 'shifting constants' sigma, which depend on the identities of both dopant and host oxides.