Europium(III)-Doped ZnO Obtained by a Hierarchically Nanostructured Multilayer Growth Strategy

A layer-by-layer growth method, named herein as impregnation–decomposition cycles (IDCs), was used to build hierarchically nanostructured multilayered nanoparticles, alternating undoped ZnO and Eu­(III)-doped ZnO layers in order to thermally induce Eu­(III) migration into the ZnO structure. Porous Vycor glass (PVG) was used as a mesoporous silica host, where the pores were used as a confined environment for preparation of ZnO nanoparticles. The proposed method allowed the control over the growth and size of the nanoparticles and prevented their coalescence. HRTEM images and XRD data revealed that ZnO nanoparticles are spheroidal with a wurtzite crystal structure and an average diameter of 4.8 nm for 10 IDCs. UV–vis DRS data indicated that the formation of ZnO nanoparticles is favored by europium­(III) doping, indicated by the band-gap absorption detection that also undergoes a red-shift by increasing the IDC number. Photoluminescence emission spectra have shown Eu­(III) intraconfigurational 4f–4f and ZnO excitonic emissions. Excitation spectra have shown energy transfers from ZnO to the silica as well as an energy transfer from ZnO to Eu­(III) ions, indicating the migration of these ions into the ZnO structure