Growth and cathodoluminescence of Eu doped ZnO nanoneedles and branched nanoneedle structures

Rare-earth (RE) ions are widely investigated luminescent centers because their intraionic-4f transitions generate narrow and intense emission lines. In this work Eu doped ZnO nanoneedles have been grown, by a thermal evaporation-deposition method, and structural and luminescence characterization has been carried out. Mixtures of ZnO and Eu2O3 or of ZnS and Eu2O3 powders were used as precursors. Annealing of the compacted powder mixtures leads to the growth of nanoneedles and nanoneedle networks, as well as rods. EDS and CL measurements enable to detect the incorporation of Eu in these structures. The choice of precursor, ZnO-Eu2O3 or ZnS-Eu2O3 influences the morphology as well as the luminescence properties of the obtained nanostructures. In particular, while in the samples obtained from ZnO, the defect green luminescence band is practically absent, the band is present in the ZnO nanoneedles obtained from ZnS. Besides the broad deep level band, a series of well-separated narrow-peaks characteristic of the intrinsic red luminescence of Eu+3 ions are observed in all cases, whose relative intensities vary from one set of samples to the other. The results suggest that the Eu3+ ions have at least, two possible configurations in the ZnO lattice with different symmetry in the nanoneedles.