Research projects:
• Investigation, through crystalline field theory, of persistent luminescence mechanisms
In this project, we will develop a spectroscopic study of crystalline systems doped with Ln3+ ions. We will be particularly interested in describing the long-lasting luminescence mechanism in these materials, via crystalline field theory, and using the time-dependent perturbation theory, to describe the lifetime and the transition probability. These quantities can help us understand this phenomenon since there is still no complete description in the literature.
Coordinator: Heveson Lima
• Synthesis, characterization and theoretical investigation of the mechanisms of TL and OSL of materials containing lanthanide ions
The study of insulating materials (crystals and glass) containing lanthanide ions (Ln) is quite extensive, due to applications in photonics. However, there is a deficiency in materials with dosimetric application as well as theoretical models that describe the behavior of thermoluminescence (TL) and optically stimulated luminescence (OSL, optically stimulated luminescence). Thus, this work proposes the development of new materials containing Ln ions for application in personal dosimetry of ionizing radiation. TL and OSL measurements will be carried out in partnership with the Energy and Nuclear Research Institute (IPEN). In parallel, atomistic calculations of these materials will be performed, using the GULP platform, to understand the load compensation mechanisms and how the defects influence the optical properties. In addition, an investigation, via crystalline field theory (CBT) and rate equations, of the TL and OSL mechanisms of materials containing lanthanide ions will be carried out. Calculations of the photoionization shock section will also be performed, to understand the population rate of electrons migrating to the conduction band.
Coordinator: Heveson Lima
Collaborators: Adelmo S. Souza and Vinicius Coelho
• Nanothermometer based on scattering light by Europium Trivalent ions Thermally Excited in Y2O3: Eu3+ Nanoparticles
Thermometers with nanometric dimensions and operating in the temperature range of 10 to 70 ° C are of great importance for biology and medicine, and their development is still a challenge for the area of thermodynamics. In this project, Rayleigh scattering by Nanoparticles of Y2O3: Eu3+ dispersed in water will be studied, in order to apply them as a nanothermometer that operates in the biological range. The study intends to experimentally obtain the relationship between the intensity of the mirrored light and the water temperature, and based on this relationship, propose a way to measure temperature using nanoparticles. The experimental part of this study will be made using an experimental apparatus built by the students of Electrical Engineering and Mechanical Engineering at UFOB during the execution of the extension project "Assembly of Measurement Systems with Arduino and Low Cost Sensors". Thus, this work intends to insert the scientific initiation student in the promising area of nanothermometer development and expand the applications of nanotechnological devices.
Coordinator: Adelmo S. Souza
• Synthesis, Structural and Magnetic Characterization of Diluted Magnetic Semiconductor Oxides, starting from Metal Salts and Using Lyophilization for Processing
It is intended to synthesize Diluted Magnetic Semiconductor Oxides (OSMD's) through freeze-drying processing and consequent appropriate heat treatments. We will start from metallic salts both to form the host matrix (for example, ZnO) and for magnetic doping (for example, Fe+3). The heat treatments will be conducted in a resistive muffle furnace, in a free atmosphere. Once the OSMD's are synthesized, they will be characterized structurally by the techniques of X-Ray Diffraction (XRD), Diffuse Reflectance Spectroscopy (ERD), as well as magnetically by the techniques of Mössbauer Spectroscopy (microscopically) and Magnetometry (macroscopically). With the results obtained from the DRX, Rietveld Refinements will be made with the Fullprof program in the structural analysis routine. With the ERD data, the system bandgaps will be obtained as-synthesized and as doped.
Coordinator: Antonio Oliveira
• Thermal, structural and magnetic study of metallic salts using freeze-drying for processing
Acetates are water-soluble salts and can easily decompose into ultrafine oxides through appropriate heat treatments. The thermal decomposition of acetates, under different heat treatment conditions, has attracted the attention of researchers due to the wide applicability involving the synthesis of ceramic compounds. These characteristics make them excellent precursors for the production of doped oxide compounds with high purity. In works previously developed by our research group (UEM's Special Materials Laboratory), aggregates of the ZnO semiconductor aggregates (finely pulverized) were made with iron acetates, cobalt or manganese. For this, we use a freeze-drying process of the heterogeneous mixture of the ZnO powder with the acetates dissolved in water. The lyophilization technique has been used for the dehydration of aqueous mixtures, resulting in a final product where the salt, in this case, presents itself homogeneously covering the aggregate, which makes it chemically more reactive with the oxide, due to the increase of its area superficial. Once freeze-dried, the mixture is subjected to different heat treatments, aiming to promote the diffusion of metals such as iron, cobalt or manganese in the ZnO (zincite) network. By replacing a small fraction of the zinc cations, which are non-magnetic, with cations of those metals (ie, Fe3+/Co2+/Mn2+), it was possible to dilute magnetic moments in the zincite network. There is great interest in these materials because they represent a new class of semiconductors called diluted magnetic semiconductors (SMD), which can plausibly exhibit ferromagnetism at room temperature. These compounds would have high technological applicability in spintronics. Taking advantage of the aforementioned characteristics of acetates, it is also possible to process (ie, lyophilize and heat treat) a mixture of two (or more) acetates, to form a nanometric ceramic, of stoichiometric composition or, eventually, with the cations of solid metal in the oxide matrix of another metal.
Coordinator: Antonio Oliveira