Near-band edge UV emission and band gap engineering of highly transparent Ba:SnO2 nanocrystalline thin films

In this paper, the structural, optical and photoluminescence (PL) features of the spray deposited Ba:SnO2 thin films with varying thickness have been investigated. X-ray diffraction analysis showed that Ba:SnO2 thin films have a polycrystalline tetragonal rutile structure and nanometric dimensions. The preferred directional growth of nanocrystalline was along <211> direction. The crystallite size of the samples was calculated using the Debye-Scherrer equation. With an increase in film thickness, the crystallite size decreased from 11.72 to 5.27 nm, while crystal imperfections, viz. lattice strain, degree of lattice distortion and dislocation density increased. The influence of film thickness on the transmittance and reflectance was investigated by using UV-Vis spectral data. The average visible transmittance of Ba:SnO2 nanocrystalline declined from 85 to 79% at 550 nm with an increase in film thickness. Ba:SnO2 nanocrystalline exhibited a slight red-shift in the absorption edge and the optical band gap was found to decrease in the range 3.94 to 3.64 eV. Near band-edge UV emissions band at ~ 402 nm were observed in the PL spectra which are attributed to the defect levels originating from the oxygen vacancies.