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Color Centers in Magnesium Doped Polycrystalline Alumina

Published online by Cambridge University Press:  21 March 2011

L. R. Brock
Affiliation:
OSRAM SYLVANIA, Research and Development, Beverly, MA 01915, U.S.A
K. C. Mishra
Affiliation:
OSRAM SYLVANIA, Research and Development, Beverly, MA 01915, U.S.A
Madis Raukas
Affiliation:
OSRAM SYLVANIA, Research and Development, Beverly, MA 01915, U.S.A
Walter P. Lapatovich
Affiliation:
OSRAM SYLVANIA, Research and Development, Beverly, MA 01915, U.S.A
George C. Wei
Affiliation:
OSRAM SYLVANIA, Research and Development, Beverly, MA 01915, U.S.A
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Abstract

We have investigated color centers in MgO-doped polycrystalline alumina (PCA) using absorption, excitation, and emission spectroscopy. Most of the color centers that were reported in earlier studies of the crystalline material have been observed to be present in the polycrystalline material. The absorption spectral features observed in the PCA are attributed to various color centers; however, they are not sufficiently resolved to make unique assignments. Suitable combinations of excitation and emission spectroscopy and also measurements at low temperature were therefore used to identify most of the color centers in this material.

Among the numerous color centers that we have identified in PCA are variations of electron centers including F, F+, F2+, F22+ and F+-Mg ((Vo-MgAl')x). The most prominent oxygen vacancy related defect observed at room temperature was the F+-Mg center, with absorption bands located at 217 and 249 nm, and an emission band at 303 nm. This center can be thought of as being formed by association of an F+ center with a Mg defect. The single crystal sapphire samples containing no Mg show only F+ (Vo) centers with 230 and 257 nm absorption bands, and a 328 nm emission band.

Low temperature (22 K) fluorescence excitation measurements of PCA led to emission from F22+center at 467 nm. Additionally, there is evidence that the observed 368 nm emission band could be attributed to the zero-phonon line associated with the F2+center.

Type
Research Article
Copyright
Copyright © Materials Research Society 2001

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