Structure and Stability of Europium Doped B-Alumina Type Phosphor
Date
2002-07
Authors
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Publisher
New York State College of Ceramics at Alfred University. Kazuo Inamori School of Engineering.
Abstract
BaMgAl10O17 (BAM) has been widely used as the host material for Eu-active
phosphors for lamps and display panels. It has a luminescent wavelength ranging from
430nm to 450nm, blue in color. However, there is a degradation problem for this
phosphor material: the luminescent intensity decreases and the emission band shifts from
blue toward green in color with an increase in application period and annealing procedure
of manufacture. The suggestion that the luminescent degradation is related to the
oxidation of europium from a 2+ to 3+ oxidation state forms the basis for the first part of
this thesis. A computer simulation study of the behavior of europium in BAM (based on
the classical Born model description the ionic materials) was carried out. Europium ions
were found to prefer different lattice positions depending on their valence state: Eu2+
prefers the BR site in the mirror plane; Eu3+ prefers the Al(2) site in the spinel block.
Because there are many other barium hexa-aluminate phases besides BAM and
because they can also be used as the phosphor host materials, the phase relationship
between these phases and the properties of the Eu dopant in these phases were also
investigated, in particular, for the barium-poor phase, Ba0.75Al11O17.25. The barium-poor
phase, after doping with Eu2+, shows a broader and shifted emission band compared to
BAM. The formation of barium-poor phase has also been proposed as the reason for the
observed luminescent degradation in BAM. Calculations on the barium-poor phase were
performed to investigate the origin of the emission band differences between it and BAM,
and the complete solid solution between them. The coexistence of multiple
OBR-distributions in the barium-poor phase was found to be the origin of the observed
broader and shifted emission band of Eu2+.
Since the hypotheses about luminescent degradation involve phase changes or
structural adjustments, molecular dynamics simulations of ion migration were also
performed to study the defect and structural changes after the europium oxidation. It was
found that Eu3+ ions can migrate from the mirror plane to the spinel block at relatively
low temperature, and that Eu2+ ions have a tendency to congregate in BAM.
Description
Advisory committee members: Paul Johnson, Doreen Edwards, Robert Condrate. Dissertation completed in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Ceramics at the Kazuo Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis