Influence of annealing temperature on photoluminescence properties and optical constants of N-doped ZnO thin films grown on muscovite mica substrates

A sol-gel spin-coating method was used to synthesize N-doped ZnO (NZO) thin films on muscovite mica substrates; the films were then annealed at 200, 300, 400, and 500 °C. The effects of the annealing temperature on their photoluminescence properties and optical constants were investigated. All the films had strong UV emissions in their photoluminescence spectra, but the green emissions at ~2.4 eV were observed only for the annealed films. The average transmittance of all the films was about 80% in the visible range and the absorption edges in the UV range at 375 nm depended strongly on the annealing temperature. The optical band gap of the films decreased gradually as the annealing temperature was increased up to 400 °C, and the Urbach energy decreased significantly as the annealing temperature increased. Finally, the various optical constants, the dielectric constant, and the optical conductivity were measured for the un-annealed film and the film annealed at 500 °C.