Effect of calcium- and/or aluminum-incorporation on morphological, structural and photoluminescence properties of electro-spun zinc oxide fibers

Pure and Al- and/or Ca-added ZnO fibers are synthesized by electro-spinning. Their morphological, structural and optical properties are investigated by means of several complementary characterization techniques, focusing attention on optical properties and fiber surface roughness, which are of relevance in many applications. The comparative analysis of the results obtained demonstrates that all the fibers consist of rounded polycrystalline oxide nanoparticles interconnected to each other, with the (dopant-dependent) nanoparticle size controlling their surface roughness. Non-stoichiometry affects all the samples and strongly influences their photoluminescence properties. Calcium segregates in a secondary phase forming calcite. On the contrary, aluminum well disperses within zincite as an isolated impurity, with Al 3+ ions substituting Zn 2+ ions in the ZnO lattice. Its content controls the relative exciton-to-defect emission band intensity, as well as the frequency of the main Zn O absorption peak.