Microstructures and luminescence properties of europium-doped CaWO4 thin films with different sputtering durations

Ca0.64WO4:Eu0.24 thin films were prepared on silicon substrates by radio frequency magnetic sputtering method. The structures, surface morphologies and luminescence properties of these thin films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and fluorescence spectroscopy, respectively. XRD analysis revealed that these films had tetragonal structure after annealing treatment at 800℃; when deposition time was over 100 min, the film grew highly preferentially in direction of (004) crystal plane. SEM studies showed that the surface of these thin films consisted of many smooth polygons. At the boundaries of crystals, some needle-like holes of about 100 nm were observed due to the overgrowth of some crystals. Under the excitation of 223 nm ultraviolet, intense and sharp emissions at 616 nm were given off from Ca0.64WO4:Eu0.24 thin films. Visible peaks situated at 592, 655 and 703 nm were observed. Moreover, positive correlativity between luminescence intensities and factors of preferential growth in the direction of (004) was confirmed. Either when the sputtering span was larger than 120 min or when the factor of preferential growth was larger than 100, strong emission could be observed. To obtain Ca0.64WO4:Eu0.24 thin films with the best properties, the optimum duration of sputtering was 140 min or so. © Editorial Board of Chinese Journal of Rare Metals. All right reserved.