Effect of the location of Mn2+ ions in the optical and magnetic properties of ZnO nanocrystals
JOURNAL OF ALLOYS AND COMPOUNDS
Authors: Batista, Elisson Andrade; Almeida Silva, Anielle Christine; de Lima, Thais Karine; Guimaraes, Eder Vinicius; da Silva, Ricardo Souza; Dantas, Noelio Oliveira
Abstract
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.
Mixed metals oxides with strong synergetic electrochemistry as battery-type electrodes for ultrafast energy storage
JOURNAL OF ALLOYS AND COMPOUNDS
Authors: Zhu, Yuanyi; Liao, Xiuxiang; Qiu, Hengrui; An, Shengli; Zhang, Yongqiang; He, Wenxiu
Abstract
The mixed metal oxides with high conductivity and multi-metal centers could easily meet the growing needs of high performance energy-storage materials. Herein, ternary phase aluminum-nickel-cobalt oxide (AINiCo-O) is facilely prepared by a hot-air oven-based method with a subsequent calcination. The as-obtained AINiCo-O flower-like network makes fully use of the synergistic effects among the transition metals, and exploits more electro-active surface sites, thereby allowing to undergo the redox reactions more efficient. The AINiCo-O electrode exhibits better charge storage performances with a remarkable specific capacity of 1008.5 C g(-1) at 1 A g(-1). Furthermore, the hybrid supercapacitor based on AINiCo-O electrode exhibits a high energy density of 63.3 W h kg(-1) at the power density of 881.4 W kg(-1), good rate capability (41.6 W h kg(-1) at 13.3 kW kg(-1)) and a satisfying cycling performance of 84.27% after 5000 cycles. This work proposes a feasible design of high-efficiency metal oxides for application in hybrid supercapacitors. (C) 2020 Elsevier B.V. All rights reserved.