The focus of the present work is the study of carbon co-deposition effect on the optical and mechanical properties of zirconia films. Optical and dielectric constant, band gap and transition lifetime of such composite systems were determined, as well as their elasticity properties. The thin ZrO2-x-C films were sputter-deposited on silicon and polycarbonate, from a pure ZrO2 and graphite targets in a radio-frequency argon plasma. Besides the zirconia phase and crystalline parameter changes induced by carbon addition, the electronic properties to the films were significantly modified: a drastical optical gap lowering was observed along an increased electronic dielectric constant and refractive index. The invariance of the film elasticity modulus and the similarity of the optical transition lifetime values with those of pure amorphous carbon films indicate an immiscibility of the ceramic and carbon components of the film structure. (C) 2007 Elsevier B.V. All rights reserved.