Apparent structural color in annealed metal oxide thin films. Interestingly, in low light the transmitted image is not colored, however the bright emission-like coloration originates from focussed illumination, and is also observable at some angles from only the fluorescent lamps light. Is it just a special case of iridescence? Has anyone seen it in sputtered films?

The films are on Corning glass substrates and are single-layer films RF sputtered from ceramic oxide targets. The apparent color which looks like emission glow does not depend strongly on the film thickness (several hundred nm), but rather just on the material type, and does not appear to be caused by simple reflection spectrum ripples. No coloration (full transparency) is seen by naked eye when looking through films in the absence of strong light.

Open discussion is welcome.