Effect of annealing temperature on optical and electrical properties of ZrO2-SnO2 nanocomposite thin films

ZrO2-SnO2 nanocomposite thin films were deposited onto quartz substrate by sol-gel dip-coating technique. Films were annealed at 500, 800 and 1,200 A degrees C respectively. X-ray diffraction pattern showed a mixture of three phases: tetragonal ZrO2 and SnO2 and orthorhombic ZrSnO4. ZrSnO4 phase and grain size increased with annealing temperature. Fourier transform infra-red spectroscopy spectra indicated the reduction of -OH groups and increase in ZrO2-SnO2, by increasing the treatment temperature. Scanning electron microscopy observations showed nucleation and particle growth on the films. The electrical conductivity decreased with increase in annealing temperature. An average transmittance greater than 80 % (in UV-visible region) was observed for all the films. The optical constants of the films were calculated. A decrease in optical band gap from 4.79 to 4.59 eV was observed with increase in annealing temperature. Photoluminescence (PL) spectra revealed an emission peak at 424 nm which indicates the presence of oxygen vacancy in ZrSnO4. PL spectra of the films exhibited an increase in the emission intensity with increase in temperature which substantiates enhancement of ZrSnO4 phase and reduction in the non-radiative defects in the films. The nanocomposite modifies the structure of the individual metal oxides, accompanied by the crystallite size change and makes it ideal for gas sensor and optical applications.