Effect of sol concentration on the structural, morphological, optical and photoluminescence properties of zirconia thin films

Abstract

ZrO2 thin films were deposited on quartz substrates from 10wt.%, 20wt.% and 40wt.% solutions of Zirconium-n-butoxide in isopropanol by sol–gel dip-coating technique. Higher concentrated sols of 20wt.% and 40wt.% exhibited faster gelation, where as 10wt.% sol remained stable for two months and films synthesized from this sol remained transparent and continuous even for 12 coatings. Ellipsometric study revealed that refractive index of the films increased with increase in sol concentration which is ascribed to the decrease in porosity. X-ray diffraction study showed that a tailoring of grain size from 7.9 to 39.2nm is possible with increase in sol concentration. Atomic force microscopy studies showed a change in growth mode from vertical to lateral mode with increase in sol concentration. The film surface revealed positive skewness and high kurtosis values which make them favorable for tribological applications. The average optical transmittance in the visible region is highest (greater than 90%) for the film deposited from 10wt.% sol. The optical band gap decreased from 5.74 to 5.62eV with increase in the sol concentration. Photoluminescence (PL) spectra of the films exhibit an increase in the emission intensity with increase in sol concentration which substantiates better crystalline quality of the film deposited from 40wt.% sol and increase in oxygen vacancies. The “Red shift” of the PL spectra with increase in sol concentration originates from the increase in the grain size with sol concentration which makes it suitable for generation of solid state lighting in light emitting diode.