Enhanced photodegradation activity of ZnO:Eu~(3+)and ZnO:Eu~(3+)@Au 3D hierarchical structures

In this work the flower-like hierarchical structures (HS) based on 3D pristine ZnO, ZnO:Eu³⁺ and ZnO:Eu³⁺@Au were successfully obtained by a template-free solvothermal and deposition-precipitation method. The decolorization/photodegradation of these structures towards model organic dye (rhodamine 6G) was studied. The synthesized ZnO-based HS were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis and photoluminescence (PL) spectroscopies. The proposed synthesis approaches allow to obtain highly crystalline 3D ZnO, ZnO:Eu³⁺ and ZnO:Eu³⁺@Au composites. Results of scanning microscopy show that ZnO flower-like HS are assemblies from smaller components, forming larger ones, the whole ZnO structure was approximately 3 μm. Au nanoparticles (size ～ 10 nm) are successfully deposited on ZnO HS surface. Luminescent studies show that ZnO is an ideal matrix for incorporation of Eu³⁺ ions in broad concentration range (Eu³⁺ = 1.0 at%–5.0 at%) with an efficient red luminescence. The strong UV emission in ZnO, as well as ZnO:Eu³⁺ HS is observed under 325 nm excitation. Doping of ZnO HS matrix by Eu³⁺ ions leads to the red shift of deep level emission peak (DLE). The PL intensity reaches the maximum up to 5 at% Eu³⁺. The photocatalytic properties of ZnO and ZnO:Eu³⁺@Au HS were investigated under UV–Vis light irradiation towards rhodamine 6G. The obtained results demonstrate the synergetic effect of the deposited gold nanoparticles and Eu³⁺ doping on photocatalytic activity of ZnO:Eu³⁺@Au HS in comparison to pristine ZnO and ZnO:Eu³⁺ HS.