Síntese e caracterização de materiais do sistema ternário SiO2-ZnO-TiO2 obtido por sol-gel/Pechini
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2014-09-24
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Universidade Federal de Goiás
Resumo
In this work the structural and optical properties of SiO2-ZnO-TiO2 system
doped with of Eu3+ (1% in mol) or Er3+ ions (0,2% to 2,0% in mol) were
investigated. The compositions xSiO2-([100-x]/2)ZnO-([100-x]/2)TiO2 with x
ranging from 40 to 80 were synthesized and studied. A mixed methodology
using the traditional sol-gel process and Pechini method was employed to
prepare stable and transparent sols, homogeneous gels, powders and
transparent thin films without cracks. The prepared powders were heat treated
from 100°C to 1100°C. The optical “band gap” values, the lifetime of Eu3+ 5D0
level, the R/O ratio of Eu3+ emissions and refractive index are dependent on the
composition and thermal treatment of the powders. Multilayered thin films were
deposited onto silica substrates using the “spin coating” technique. Afterwards,
the as-prepared thin films were calcined at 500°C followed by annealings from
700°C to 1000°C. The X-ray diffraction of powders showed that the
crystallization starts at 800°C with a mixture of zinc titanate phases (ZnTiO3,
Zn2TiO4) and titanium rutile (TiO2). In compositions with low silica content (x =
40 or 50) the formation of zinc silicate (Zn2SiO4) occurs at high temperatures.
The optical properties were evaluated for both powders and thin films.
Particularly, thin films exhibit transmittance above 80% in the visible region. The
refractive index at 632.8 nm and thickness of thin films were estimated using
the envelope method and m-Line spectrocopy. Furthermore, morphological
analysis of the thin films surface was performed by scanning electron
microscopy. The characteristic emission peaks of Er3+ or Eu3+ doped powders
and thin films were measured. The photoluminescent emission of Eu3+ ions,
obtained the highest intensities for the powders treated at 800°C, for films
treated at 700°C, under excitation at 394 nm, where the system remains
primarily amorphous. The photoluminescent emission of the Er3+ ions was more
intense for the powders treated at 1100°C under excitation at 980 nm, mainly
due to reduction of hydroxyl groups which act as photoluminescence
quenchers. In the film the highest intensity occurred at a temperature of 700°C
under excitation at 378 nm and showing only one guided mode. Thus, the
obtained thin films can be suitable for application as waveguides in integrated
optical systems. Moreover, the Eu and Er doped powders can be used as
phosphors in displays.
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Citação
ALMEIDA, Michelly Patrícia Santana de. Síntese e caracterização de materiais do sistema ternário SiO2-ZnO-TiO2 obtido por sol-gel/Pechini. 2014. 162 f. Tese (Doutorado em Química) - Universidade Federal de Goiás, Goiânia, 2014.