• Cation substitution induced blue-shift of optical band gap in nanocrystalline Zn$_{(1−x)}$Ca$_x$O thin films deposited by sol–gel dip coating technique

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      Transparent nanocrystalline Zn${(1−x)}$Ca$_{x}O ($0 ≤ x ≤ 0.20$) thin films were deposited on glass substrates by sol–gel dip coating method. The X-ray diffraction (XRD) pattern revealed the polycrystalline nature of the films withhexagonal wurtzite structure and confirmed the non-existence of the secondary phase corresponding to CaO indicating the monophasic nature of the deposited films. The crystallinity of the films deteriorated with higher dopant concentration due to the segregation or separation of dopant ions in grain boundaries. The lattice parameters and the unit cell volume increased to a higher Ca-dopant concentration. This was due to the successful incorporation of Ca2+ ions with larger ionic radius inthe host zinc oxide (ZnO) lattice. The optical transmittance spectra of the samples showed transmittances above 60% in thevisible spectral range and the absorption edge in the near ultra-violet region got blue-shifted with cation substitution. Theestimated optical energy gaps confirmed the band gap widening with increase in Ca-dopant concentration. The calculatedvalues increased from 3.30 eV for undoped ZnO to 3.73 eV for Zn0.8Ca0.2O thin films giving 13.03% enhancement in theenergy gap value due to the electronic perturbation caused by cation substitution as well as deterioration in crystallinity.

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      1. Department of Physics, Kannur University, Payyanur Campus, Edat P.O., Kerala 670327, India
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  • Bulletin of Materials Science | News

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