Optical constants and near infrared emission of Er doped ZnO sol–gel thin films

Erbium (Er) doped zinc oxide (ZnO) sol–gel thin films were deposited on glass substrate using the spin coating method. The effect of erbium concentration and annealing temperature on structural and optical properties was studied. The annealed film was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrum (EDX), micro-Raman, photoluminescence (PL) and UV–vis spectroscopy. All the films showed a wurtzite structure of polycrystalline nature with an average crystal size of 27.44nm at 500°C and 29.28nm at 600°C. The Raman spectra confirmed the absence of secondary phases in the Er doped ZnO films and the longitudinal optical phonon mode was upto the fifth order. Densely packed surfaces of the films were observed from SEM images. The presence and distribution of Zn, O and Er elements in the deposited films were confirmed by EDX analysis. The calculated value of exciton binding energy of ZnO film was 60meV with a maximum value of 72meV being observed for Er doped films. The near infra-red emission peak was observed at 1.63eV through PL spectra studies. The average transmission was 80% with the calculated value of optical band gap being 3.26–3.32eV. An increase in the refractive index value predicts the substitutional incorporation of Er ions in ZnO with the maximum optical conductivity being observed in the UV region. •Higher exciton binding energy in the doped ZnO films.•Near infrared emission is observed and better than ZnO.•Refractive index is calculated by theoretical and experimental means.•Maximum optical conductivity in the UV region.