The transmittance spectra of the films were recorded in the
UV–vis region. It was found that all the films were highly
transparent in the visible region having greater than 90%
transmission. Inset of Fig. 3 illustrates the spectral variation
of samples 1a–1f. For all the films, there is a sharp rise in transmittance
up to 98% in the UV region followed by decreases to
95% and it remains constant in the visible region.
Similarly, inset of Fig. 4 shows the transmittance of films
2a–2f in which all the films exhibit a sharp rise up to 90% in
UV region and remained constant in the visible region. The
difference in observed transmittance of films may be ascribed
to disparity in surface morphologies, crystallite size and existence
of surface defects causing a decrease in transmittance
due to scattering of light. Moreover, red shift in the transmission
edge was observed with decreasing thickness of the films
and increasing calcination temperature.