Effect of the location of Mn2+ ions in the optical and magnetic properties of ZnO nanocrystals

Intrinsically stable metal oxide systems, such as nanosized zinc oxide (ZnO), offer an ideal template for the production of transition metal (TM)-doped structures or diluted magnetic semiconductor (DMS) nanocrystal. Then, a systematic study of possible candidates and a study of the coordination geometry in which the TM ions meet, are key points for success, this being the focus of the present study, which contains promising information that can be used to develop magneto-optics devices. In this work, we investigated the coordination geometry in which the Mn2+ ions are localized into ZnO nanocrystals (NCs) in function of the concentration of Mn and how it affects the structural, morphological, optical and magnetic properties. The physical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-Ray spectrometry results (EDS), UV-Vis-NIR spectroscopy, Fluorescence (FL), and Electron Paramagnetic Resonance (EPR). To investigate the location and oxidation of Mn ions in the ZnO crystalline structure, the crystalline field theory in the optical absorption spectra, and EPR results were used. XRD patterns confirmed Mn2+ doped ZnO and that higher Mn concentrations occur in the formation of ZnMn2O4 NCs. SEM images show that the doping process does not affect particle morphology, but in higher Mn concentrations occur the formation of the two morphologies. FL spectra show how the coordination geometry in which the Mn2+ ions are located alters the luminescence properties. The energy transfer process between ZnO NCs and Mn2+ ions, with the transition T-4(1) <- (6)A(1), is observed. The luminescent intensity from Mn2+ ions shows a linear increase followed by a decrease as a function of Mn doping. In the EPR spectra confirmed the incorporation of Mn2+ ions at interior and surface of the ZnO NCs, with the Mn concentration. Therefore, the study of the development of DMS is a powerful tool for designing new materials with tuned magneto-optics properties as a function of the TM ions concentration. Published by Elsevier B.V.