Effect of Eu doping on the near band edge emission of Eu doped ZnO thin films after high temperature annealing

We studied the effect of europium (Eu) doping on the near band edge emission of ZnO thin films, fabricated by sputtering and high temperatures annealing. The doping concentration of Eu in the ZnO films was varied from 0.01 to 0.62 at.%. Photoluminescence (PL) spectra showed that the films ultra-violet (UV) emission was enhanced very much by high temperature treatment and was stronger for the Eu doped ZnO than that for the undoped ZnO films after 1100 degrees C annealing. X-ray diffraction showed the films had hexagonal wurtzite structure, the width of the ZnO (002) plane diffraction peak was sensitive to the anneal temperature and also to the Eu doping concentration, and Zn silicates had formed after the 1100 degrees C annealing. Scanning electron microscopy showed that the surface morphology of the films became more uneven with increasing Eu concentration. The PL decay spectra inferred that the lifetime of the UV PL was correlated with the size of ZnO nanocrystals in the films. The results support that the intensity of the UV PL is primarily influenced by the crystalline perfection of the films which is also influenced by the Eu doping concentration.