Low cerium doping investigation on structural and photoluminescence properties of sol-gel ZnO thin films

Undoped and cerium (Ce)-doped zinc oxide (ZnO) thin films with various doping concentrations of cerium (0.1-0.9 at.%) were prepared on glass substrates by the sol-gel dip-coating process. The effects of Ce doping on the structural, morphological and optical properties were studied by X-ray diffraction, energy-dispersive X-rays, atomic force microscopy, UV-visible spectrophotometry and photoluminescence spectroscopy. The diffraction patterns showed that all the samples are characterized by a hexagonal wurtzite crystalline ZnO structure with (0002) preferred orientation. The crystal quality and crystallite size were found to decrease with the Ce doping level. From the atomic force microscopy images analysis it was revealed that both of the grain size and the surface roughness decrease with the increasing of the Ce concentrations. According to UV-visible measurements all the films are highly transparent with average visible transmittance values ranging from 79% to 82%, and the optical band gap is sensitive to the dopant concentration. Room temperature photoluminescence spectra put into evidence that UV and visible emissions decrease significantly as the Ce concentration increases from 0.1 to 0.9 at.%.