Blue shift in optical band gap of sol–gel derived Sn1−xZnxO2 polycrystalline thin films

Abstract

Undoped and Zn doped SnO2 thin films are deposited by sol–gel spin coating on glass substrate. XRD spectra with prominent peaks along (110) and (101) planes shows the polycrystalline nature of thin films. The particle size lies between 9.30 and 42.09 nm as estimated by Debye–Scherer method. SEM micrographs of the films contain pebble like structures spread throughout whose diameter decreases with increase in dopant concentration. Surface topology of the films is studied by atomic force microscopy. Transmission spectra show that all the films are highly transparent in the visible and IR spectral region (80–90 %) and a sharp absorption occurs near 300 nm. Approximately a change of 4 % is observed in the optical band gap by Zn doping. The optical band gap is tunable between 3.55 and 3.68 eV for 0 ≤ x ≤ 0.15 in nanocrystalline Sn1−xZnxO2. Broad UV emission at 395 nm is observed in photoluminescence spectra of the films along with a blue emission. Emission intensity decreases as amount of Zn incorporated into SnO2 increases.