Self-assembled nanostructured ZnO hollow spheres with UVA luminescence

Nanostructured ZnO hollow spheres with average crystallite size of ∼50 nm, particle size distribution in the range of 600-2000 nm and a typical shell thickness of about 300-700 nm, were successfully fabricated through a facile hydrothermal route, using triethanolamine (TEA, C₆H₁₅NO₃) as a morphology control agent and pH as the structural involved parameter. Hollow spheres were formed due to self-assembled aggregation of zinc ion complexes and formation of internal voids with Ostwald ripening mechanism. These internal spaces can be filled and the spheres may enlarge, due to diffusion of the ionic complexes of the solution toward the surface of the initial particles and Kirkendall effect. This phenomenon was supposed to cause the mentioned size distribution in the outer diameters of the hollow spheres and their internal voids. The fabricated nanostructured spheres showed an ultraviolet A (UVA) luminescence and an intense yellow emission in the visible band which can be attributed to the low density of oxygen defects on the surface of the synthesised particles.