Band gap and superior refractive index tailoring properties in nanocomposite thin film achieved through sol-gel co-deposition method

Transparent nanocomposite ZrO2-SnO2 thin films with molar ratio 0.1/0.9 (ZS19), 0.3/0.7 (ZS37), 0.5/0.5 (ZS55), 0.7/0.3 (ZS73) and 0.9/0.1 (ZS91) of ZrO2/SnO2 were prepared by sol-gel dip-coating technique. X-ray diffraction (XRD) spectra showed a mixture of three phases: tetragonal ZrO2 and SnO2 and orthorhombic ZrSnO4. X-ray photoelectron spectroscopy (XPS) gives Zr 3d, Sn 3d and O1s spectra on ZS55 thin film which revealed the presence of oxygen vacancies in the nanocomposite ZrO2-SnO2 thin film. Scanning electron microscopy (SEM) observations showed that microstructure of ZS55 consists of uniformly dispersed isolated SnO2 particles in ZrO2 matrix. An average transmittance greater than 85% (in UV-visible region) is observed in the films ZS55, ZS73 and ZS91, but superior optical properties was observed in ZS55 thin film. The composite system under certain compositional mixings (ZS55) displayed a refractive index supremacy over pure zirconia films which can be directly employed in extending the range of tunability of the refractive index. Besides, these films also demonstrated tailoring of band gap values. Photoluminescence (PL) spectra revealed an intense emission peak at 424 nm in ZS55 sample which indicates the presence of oxygen vacancies in ZrSnO4. All these characterizations distinctly indicate a strong interrelation between the microstructural ordering and superior optical properties of the present ZrO2-SnO2 co-deposited composites. (C) 2011 Elsevier B. V. All rights reserved.