Thin Pd-capped rare-earth metallic films switch reversibly from their initial reflecting state (metal phase) to visually transparent state (insulator or semiconductor phase) when exposed to gaseous hydrogen. Palladium-capped Gadolinium films were prepared by rf-sputtering technique to produce very homogeneous and high-quality metal films as indicated by X-ray and scanning electron microscope analysis. After preparation, a separate cell and experimental setup are used that allow both optical and electrical measurements of the films during hydrogen loading simultaneously. The thickness dependence of the switching properties of Gadolinium hydride system is presented. The complex refractive index, the thickness, as well as the energy gap, of GdH3 films (transparent phase) were calculated from transmission data by use of a new technique based on "Forouhi-Bloomer" model, and by a recent "pointwise unconstrained minimization approach" method. (c) 2005 Elsevier B.V. All rights reserved.