Evolution of surface morphologies of CaMoO4 films and their luminescent properties

Alkaline earth molybdate and tungstate thin films are widely prepared by electrochemical methods. In solutions, these crystals often grow into large clusters. Hence, it is difficult to obtain nanomolybdate and tungstate thin films via electrodeposition. The morphologies of CaMoO4 thin films synthesized by galvanic cell route at different stages were compared and characterized. Scanning electron microscope (SEM) observations reveal that CaMoO4 thin films consist of two layers, sub-layer and top layer. Atomic force microscope (AFM) examination confirms that the roughness of sub-layer is within several nanometers. Both AFM analysis and the calculation based on XRD results favor that the average size of CaMoO4 crystallites is approximately several tens of nanometers. The top layer is usually rough due to large crystals in shapes of pyramids. Fluorescent study shows that the luminescence intensities of samples only with smooth layers are about four times of those filled with micrometer-sized CaMoO4 crystals. The reason accounting for the improvement of luminescent properties may lie in that there are much less lateral scattering for smooth samples.