Page 342 - 00. Complete Version - Progress Report IPEN 2014-2016

342 Materials and Nanotechnology | Progress Report

common. In the actual research BaAl2O4 materials were prepared: Eu2 + , TR3 + through the ce-
ramic methods and combustion, and CdSiO3 : TR3 + ( TR : Y , La , Ce , Pr , Nd , Sm, Eu , Gd , Tb , Dy
, Ho , Er , Tm , Yb , Lu ) , by ceramic method, showing persistent luminescence property. As usu-
al, the combustion synthesis produces crystals with smaller size, evidently due to higher local
temperature during the spontaneous explosion. Since the thermoluminescence analyses sug-
gested the presence of one and three traps for the combustion and solid state prepared materi-
als, respectively, the method of preparation has a significant influence on the defect structure
of the materials. BaAl2O4 : Eu2+ , TR3+ and CdSiO3 : TR3 + materials were investigated by ab-
sorption spectroscopy in the infrared, scanning electron microscopy , absorption spectrosco-
py, X-ray structure were studied by absorption of X-rays near the edge- XANES absorption fine
structure and X-ray extended - EXAFS other than electron excitation and emission spectrosco-
py in the regions of UV and vacuum - UV- vis and thermoluminescence. It was also investigate
the photoluminescence properties of their excitation and emission spectra, the lifetime of ex-
cited states and the positions of the ground states of the ions TR2+/3+ in the Band Gap. Mecha-
nisms were discussed for the persistent luminescence phenomenon of Eu2+ ion doped in BaA-
l2O4 matrix and TR3+ ions doped in CdSiO3 matrix. The mismatch between the band gap (Eg)
value obtained from the synchrotron radiation excitation spectra and the DFT calculation was
deduced to results from the covalent bonding in the BaAl2O4 host. The XANES spectroscopy
showed a predominance of Eu3+ which can be present as a result of the in situ conditions of
persistent luminescence during the X-ray irradiation. (Figure. 68).

Multiferroic properties in rare earth doped oxide thin films

For the last few decades, the consumption of electronic devices and the high demand for data
storage have shown great opportunities to create modern technologies that assure the world-
wide needs in computing development. Some multiferroic materials have been extensively stud-
ied. The BiFeO3 is considered the only one that has at least two ferroic at room temperature, so
that it has received special attention as a candidate to produce logic and memory devices. The
use of growth techniques such as pulsed laser deposition allowed the production of thin films
with high quality control. Multiferroic thin film heterostructures of BiFeO3 and LaBiFeO3 were
grown to evaluate and test their electrical and magnetic properties. The multiferroic project was
developed at the University of California - Berkeley covered by the Everton Bonturim doctoral
project and his supervisor Professor R. Ramesh, looking to improve the state-of-the-art in de-
vices technologies through the pure and applied nanoscience (Figure. 69).

Figure 69 – In-plane
PFM image with its vec-
tor component of the
domain structure (a)
and the electrical hys-
teresis loops at dif-
ferent frequencies (b)
of a ferroelectric thin
film heterostructures
grown via physical
deposition technique.

Instituto de Pesquisas Energéticas e Nucleares