Effect of calcination atmosphere on photoluminescence properties of nanocrystalline ZrO2 thin films prepared by sol-gel dip coating method

Highly transparent and homogeneous nanocrystalline ZrO2 thin films were prepared by the sol-gel dip coating method. The X-ray diffraction (XRD) pattern of ZrO2 thin films calcined in air, O-2 or N-2 shows the formation of tetragonal phase with varying crystallite size. X-ray photoelectron spectroscopy (XPS) gives Zr 3d and O 1s spectra of thin film annealed in air, which reveal zirconium suboxide component (ZrOx, 0 < x < 2), Zr-O bond and surface defects. An average transmittance greater than 85% (in UV-vis region) is observed in all calcined samples. Photoluminescence (PL) reveals an intense emission peak at 379 nm and weak peaks at 294, 586 and 754 nm for ZrO2 film calcined in air. An enhancement of PL intensity and red-shift is observed in films calcined in O-2 and N-2 atmosphere. This is due to the reconstruction of zirconium nanocrystal interfaces and vacancies, which help passivate the non-radiative defects. The oxygen deficient defect, which is due to the distorted Zr-O bond, is suggested to be responsible for photoluminescence. The defect states in the nanocrystalline zirconia thin films play an important role in the energy transfer process. The luminescence defects in the film make it suitable for gas sensors development and tunable lasers. (C) 2011 Elsevier B.V. All rights reserved.