Synthesis and characterization of sol-gel derived La and Sm doped ZnO thin films: A solar light photo catalyst for methylene blue

Sol-gel spin coating method have been used to deposit un-doped, La, and Sm-doped ZnO thin films on Si substrate. The influence of Sm and La doping content on various physical properties of ZnO thin films were investigated using x-ray diffraction, photoluminescence spectroscopy, spectroscopy ellipsometry, scanning electron microscope, and four point probe technique. X-ray diffraction analysis reveals that Sm and La ions were successfully incorporated in ZnO lattice and all the thin films are highly crystalline with hexagonal wurtzite structure. Photoluminescence spectroscopy spectra indicates that defect concentration increases on increase in Sm and La content. Refractive index, extinction coefficient and optical band gap were determined from spectroscopy ellipsometry technique. The optical bandgap of ZnO thin films shifts towards higher wavelength (red shift) on incorporating La and Sm because of which its absorption ability for visible portion of electromagnetic radiation increases. The micrographs obtained from scanning electron microscope reveals that morphology consists of wrinkle type structure; the density of the wrinkles seems to be dependent on the dopant concentration as well as on the type of dopant. Remarkable improvement in electrical conductivity have also been observed after doping. Sm-and La-doped ZnO thin films have shown better photocatalytic degradation efficiency for methylene blue under solar light irradiation.