Enhancement of the photochromic and thermochromic properties of molybdenumoxide thin films by a cadmium sulfide underlayer

We investigated the photochromic and thermochromic behavior of amorphous Mo O3 films prepared by thermal evaporation of MoO3 powder on glass and glass/ CdS substrates. We used the cadmium sulfide as a carrier charge injector to produce higher color center concentrations in the MoO3 film. The semicondu ctor CdS (cadmium sulfide) film was synthesized using the chemical bath dep osition technique. The glass/MoO3 and glass/CdS/MoO3 films were subjected t o tungsten lamp (100 W) exposure times of 45 to 180 min to study the photoc hromic sensitivity of the films. To study the thermochromic properties, sam ples were thermally annealed at temperatures ranging from 100 to 250 degree s C during 2 h. X-ray diffraction studies show that the CdS films were poly crystalline, and the oxide films were amorphous. Optical absorption measure ments showed the presence of an absorption band centered around 850 nm due to the formation of color centers. Concentrations of these were calculated using the Smakula equation. Results indicate that the addition of CdS films enhances the photochromic and thermochromic properties of MoO3. Photochrom ism is more effective than thermochromism in generating color centers when using CdS as a charge carrier.