PPGF/CCET

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE: NAVADEEP SHRIVASTAVA
DATA: 01/12/2017
HORA: 14:00
LOCAL: Auditório do prédio da Pós-Graduação
TÍTULO: Development of Magnetic-Luminescent Bifunctional Nanomaterials and Their Application in Radiation Detection
PALAVRAS-CHAVES: Bifunctional materials, magnetism, photoluminescence, Inorganic Rare Earth materials, Quantum dots, Scintillation
PÁGINAS: 118
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Materiais Magnéticos e Propriedades Magnéticas
RESUMO: The preparation of novel triply-doped bifunctional Fe3O4/ZnS@LaF3:xCe3+, xGd3+, yTb3+(x = 5; y = 5, 10 and 15 mol. %) nanocomposites with efficient optical and magnetic features have been reported. The ZnS semiconductor functionalized Fe3O4 particles were coated with LaF3:RE3+materials via chitosan assisted co-precipitation method. A core of size ~ 7.2 nm and trigonal structure of bifunctional nanostructure were confirmed from x-rays diffraction and high resolution transmission electron microscopy along with HAADF imaging. The static magnetic measurements supported and manifested superparamagnetic behavior of the materials at 300 K. A broad emission band was observed in the blue region (400-550 nm) due to the sulphur vacancy on the surface of Fe3O4/ZnS nanocomposites. For triply doped bifunctional nanostructure, the excitation spectra revealed broad absorption bands centered at 270 nm, which attributed to the 4f(7F7/2)5d interconfigurational transition of the Ce3+ ion accompanied by narrow absorption lines arising from the 4f–4f intraconfigurational transitions of the Tb3+ ion. The emission spectra of the nanocomposites showed characteristic narrow emission lines assigned to the 5D47FJ transitions (J = 6-0) of the Tb3+ ion. The energy transfer process from the Ce3+Gd3+Tb3+ ions was also presented and discussed. Further, the structural, photoluminescence and magnetic properties of Fe3O4/ZnS@LaF3:RE3+ suggested efficient candidature for the magnetic light-converting molecular devices (MLMCDs) and high energy radiation detection. Next a new triply doped multi color tuned photonic nanomaterial based on LaF3:Ce3+,Gd3+,Eu2/3+ has been prepared by simple polyol method. Hexagonal phase of LaF3:xCe3+,xGd3+,yEu3+with average size (4-6 nm) was confirmed by X-ray diffrcation and high resolution electron microscopy. An EDS mapping analysis showed the uniform distribution of Ce3+,Gd3+ and Eu2/3+ dopants in the LaF3 host matrix. The existence of Eu2+ ions was confirmed by X-ray absorption spectroscopy as well as by photoluminescence spectra. Magnetic investigation of the nanomaterials confirmed the paramagnetic features at room temperature, whereas a weak ferromagnetic ordering is observed 2 K. Triply doped LaF3 nanoparticles showed a broad range of photoluminescence peaks covering UV-Visible region after excitation at 260 nm. The Judd–parameters were calculated extensively and showed the greatest efficiancy of 85% of the LaF3:xCe3+,xGd3+,yEu2/3+ (x= 5, y= 10 mol%). The multicolor tuning of these nanomaterials may have potential applications as scintillating materials in high energy radiation detection, the reason being Ce3+/Eu2+ as gamma ray sensitizer, Gd3+ as highest stable cross section of neutron captor and Eu2+/Eu3+ as luminescence activator or wavelength shifter in the visible region.
MEMBROS DA BANCA:
Interno - 1925296 - ALAN SILVA DE MENEZES
Externo à Instituição - CARLOS JACINTO DA SILVA - UFAL
Externo à Instituição - JOSE ANTONIO HUAMANÍ COAQUIRA - UnB
Externo ao Programa - 2062073 - MARCIO AURELIO PINHEIRO ALMEIDA
Presidente - 2197864 - SURENDER KUMAR SHARMA