https://ri.ufs.br/jspui/handle/riufs/2467 2026-07-30T07:42:04Z 2026-07-30T07:42:04Z Oliveira, Renato Willy Vieira de https://ri.ufs.br/jspui/handle/riufs/25434 2026-07-09T17:49:23Z 2026-02-04T00:00:00Z

Título: Análise teórica das propriedades térmicas das matrizes de Y2O3, YF3 e Y7O6F9, dopadas com Nd3+ via modelagem computacional Autor(es): Oliveira, Renato Willy Vieira de Abstract: In this work, classical atomistic computational modeling techniques and crystal field theory studies were applied to the case of yttrium oxide (Y2O3), yttrium fluoride (YF3), and yttrium Voxyfluoride (Y7O6F9) matrices doped with neodymium lanthanide ions (Nd3+) from the perspective of thermometric variations within the temperature range of 273 K to 373 K, whose applications are based on thermometry in the biological window. The study was initially based on the interatomic potential model and the lattice energy minimization method. For the set of potentials used to simulate the crystal structures studied, an agreement above 97.9% was obtained for Y7O6F9, 98.7% for Y2O3, and 98% for YF3 within the proposed thermal scales. From this, the incorporation of the Nd3+ ion was carried out following the Mott-Littleton method, through isovalent substitution, in which the neodymium ion directly replaces the Y3+ ion in the matrices. For the Y2O3 and Y7O6F9 lattices, the Y3+ sites with the highest probabilities of neodymium incorporation into the matrix were evaluated. From these results, it was possible to note that the first Y3+ site (Y1) will have the lowest solution energy in the Y2O3 matrix, while for the Y7O6F9 matrix, the Y1 and Y2 sites have similar probabilities of neodymium incorporation. YF3 has only one available Y3+. From the atomistic modeling study, it was possible to perform crystal field theory calculations for the crystalline matrices studied. The calculation performed consists of applying two models found in the literature to obtain the results of the crystal field parameters, the PCEM and SOM models. In these calculations, it was possible to observe the electrostatic interaction in each matrix, and, after that, calculations of crystal field forces were performed. Crystal field forces were calculated from the rotational invariants. From these calculations, it was possible to define the limits of the spectroscopically active coordination spheres of neodymium at each site in the three crystalline matrices. Starting from the crystal field parameters, the energy levels of the ground state of Nd3+ , 4 I9/2, and the excited state, 4F3/2, were calculated. From the results obtained for the energy levels, it was possible to evaluate the thermal sensitivity from the variation between the energy levels of the excited state, correlating them to Boltzmann statistics.

2026-02-04T00:00:00Z Santos, Marcelo Franklin da Silva https://ri.ufs.br/jspui/handle/riufs/25433 2026-07-09T17:48:55Z 2026-02-04T00:00:00Z

Título: Síntese e caracterização estrutural, morfológica, elementar e dosimétrica de CaSO4:Tm,Li preparado por evaporação lenta, coprecipitação e difusão em estado sólido Autor(es): Santos, Marcelo Franklin da Silva Abstract: Calcium sulfate (CaSO₄) based thermoluminescent dosimeters are widely used in ionizing radiation dosimetry, with CaSO₄:Dy being particularly noteworthy. In this study, the structural, thermal, morphological, elemental, and dosimetric properties of CaSO₄ phosphors doped with thulium (in metallic and oxide forms) and co-doped with lithium, produced by slow evaporation synthesis (SEL), solid-state diffusion (SES), and coprecipitation (PRE) syntheses, were investigated. The work involved the preparation and characterization of the phosphor. For structural characterization, X-ray diffractometry (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used. For dosimetric characterizations, thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques were used. The samples in the form of pellets were irradiated with a ⁹⁰Sr+⁹⁰Y source in the dose range of 0.142 Gy to 500 Gy. XRD analyses confirmed the formation of the CaSO₄ crystalline phase for all production routes, SEM analyses revealed significant morphological differences between the materials obtained by the different routes, and EDS analyses confirmed the incorporation of thulium into the compounds. The CaSO₄ samples produced by SEL showed significantly higher TL and OSL intensities than those obtained by SES and PRE. The TL emission curves exhibited multiple peaks, with predominant emissions in the blue region (455 nm), characteristic of Tm³⁺. Co-doping with lithium contributed to intensifying the luminescent signal of the samples. The OSL curves exhibited typical exponential decay for all samples, with the samples obtained via SEL exhibiting slow decay emission, indicating low photoionization cross section and charge transfer in the blue LED stimulation process. All CaSO₄:Tm,Li phosphors exhibited homogeneous TL and OSL responses to the dose (with a coefficient of variation less than 10%), adequate response linearity for the dose range studied, and TL signal stability for traps associated with peaks above 200 °C (fading). The results indicate that the CaSO₄:Tm,Li compound, especially when synthesized by slow evaporation, has high potential for applications in ionizing radiation dosimetry. Complementary studies, such as assessments of energy dependence, lower dose detection limit, and longer fading periods, will contribute to a comprehensive evaluation of its dosimetric performance, will contribute to a comprehensive evaluation of its dosimetric performance.

2026-02-04T00:00:00Z Santos, José Alex Vieira dos https://ri.ufs.br/jspui/handle/riufs/25432 2026-07-09T17:48:34Z 2026-02-12T00:00:00Z

Título: Síntese de nanoestruturas de óxido de ferro para aplicações em hipertermia magnética Autor(es): Santos, José Alex Vieira dos Abstract: In this work, the structural and magnetic properties of iron oxide nanoparticles synthesized via the hydrothermal method were investigated. Sodium phosphate and sodium sulfate were added to control the morphology of the nanostructures. A reduction process using a gas mixture (N2 95% - H2 5 was employed to ensure the formation of the magnetite phase (Fe3O4) in the final samples. Structural characterization was performed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns confirmed the crystalline Fe3O4 phase in all studied samples. The average size of the crystallites, estimated by the full width at half maximum of the XRD peaks extracted from the Rietveld refinement and using the Scherrer equation, indicated that nanoparticles diameters are in the range from 22 to 40 nm range. TEM images revealed morphologies such as spheres, rods, tubes, and rings, depending on the phosphate/sulfate ratio. Magnetic characterization included magnetization measurements as a function of field (M vs. H) and temperature in the Zero Field Cooling – Field Cooling (ZFC/FC) mode. These results indicate that the nanoparticles are not in a superparamagnetic state at room temperature, suggesting sizes larger than the typical magnetic single-domain limit. Furthermore, the data point to a highly interacting system. Magnetic hyperthermia measurements, conducted under an AC magnetic field of 32 kA/m and a frequency of 311 kHz, showed a temperature increase of 7 °C within 100 to 200 s. Analysis of these results yielded Specific Absorption Rate (SAR) values between 260 to 510 W/g. Notably, the sample with ring-like morphology proved to be the most promising for hyperthermia treatment applications.

2026-02-12T00:00:00Z Banda, Geraldine https://ri.ufs.br/jspui/handle/riufs/25423 2026-07-09T17:44:47Z 2026-02-09T00:00:00Z

Título: Study of the spectroscopic properties of Thulium doped in Yttrium Ytterbium Gallium Garnet (YYbGG) crystals Autor(es): Banda, Geraldine Abstract: Rare earth elements have been extensively investigated owing to their unique optical properties, which arise from intra-4f electronic transitions and are strongly influenced by both the dopant ion and the host crystal matrix. Among these materials, thulium-doped yttrium ytterbium gallium garnet (Tm:YYbGG) has attracted attention due to its potential for multifunctional luminescent applications. In this study, Tm:YYbGG crystals synthesised via a nucleation and growth process were systematically investigated to evaluate their spectroscopic and thermometric properties. Under excitation at 800 nm and 980 nm, the material exhibited both downconversion and upconversion luminescence, demonstrating emissions in the visible and near-infrared (NIR) spectral regions. Power-dependent measurements confirmed multiphoton processes under upconversion and down conversion excitation, while temperature-dependent studies were conducted over the range 303–373 K to assess thermometric performance. Six distinct emission bands were observed, including visible emissions at 485 nm (blue), 650 nm (red), and 685 nm (deep red), as well as NIR emissions at 1050 nm, 1450 nm, and 1650 nm. The luminescence intensity ratio (LIR) technique was applied to transitions originating from nonthermally coupled levels to determine temperature sensitivity. The relative sensitivity values were found to range from 0.72 to 1.02 % K−1 under downconversion excitation and from 1.64 to 2.26 % K−1 under upconversion excitation. The enhanced sensitivity observed under upconversion excitation indicates improved thermometric performance. These findings demonstrate that Tm:YYbGG crystals exhibit stable and efficient luminescence behaviour, highlighting their potential as promising candidates for optical temperature sensing applications

2026-02-09T00:00:00Z