INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Luminescent materials based on Ceria, gadolinium and europium oxides
Autor/es:
CECILIA SORBELLO; BEATRIZ C. BARJA; MATÍAS JOBBÁGY
Lugar:
La Plata
Reunión:
Congreso; Congreso; 21th I-APS Interamerican Photochemical Conference; 2011; 2011
Resumen:
Lanthanides are widely used to develop solid luminescent materials (phosphors) with technological applications in the field of light conversion: luminescent lamps, diodes, and optical fibers for telecommunications.[i]. These ions display a well-defined luminescence characterized by very narrow (a few nm) and highly structured emission bands with lifetimes in the millisecond timescale. Their almost monochromatic emission makes them especially useful for optical purposes. In this work luminescent microparticles (average 100 nm) were synthesized with the homogeneous phase precipitation method through the thermal hydrolysis of urea with a high control of morphology and size. The control of these characteristics is particularly useful to develop luminescent solid materials to fabricate luminescent screens. The structural and emission properties of a family of oxides (Ce1-x  Gdx) with a fixed amount of Eu(III) were studied for x = 0, 0,05, 0,10, 0,25, 0,50, 0,75 and 1,0. The amorphous precursors obtained by controlled heating at 90oC were finally filtered, dried and calcinated at 1000oC in air. The techniques used to characterize these particles were stationary emission spectroscopy (at room temperature and 77 K), powder X-Ray diffraction and high resolution scanning electron microscopy (HRSEM) coupled with dispersive energy X-Ray diffraction (EDS). The band assignment for the intra 4f-f transitions of Eu(III) and Gd(III) as well as for the charge transfer transitions of Eu(III) and Ce(IV) was performed and the energy transfer mechanisms were analyzed.     The graph shows the excitation spectra of three Ce(IV)/Gd(III) oxides with 5% Eu(III) for lem= 612 nm. The bands correspond to the 7F0®5DJ (J= 0,1,2,3,4) and 7F0®5L6 Eu(III) transitions. From the graph it can be observed that an increase in the Ce(IV) does not yield the corresponding proportional increase in the intensities of the Eu(III) bands. This result together with the change in the profiles of the bands indicate that the Eu(III) sense changes in the environment in which it is located. Considering that the Gd2O3 oxide has a c-type structure (C2 and S6 sites) and that CeO2 has an octahedral fluorite structure (Oh), the analysis of these bands for different x values can help elucidating the actual structure of the binary system as a complimentary alternative to the X-Ray technique. [i] W. M. Yen, Sh. Shionoya y Hajime Yamamoto. Phosphor Handbook, CRC Press, 2007  
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