University of Khartoum

The impurity levels of lanthanide ions in silica

The impurity levels of lanthanide ions in silica

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Title: The impurity levels of lanthanide ions in silica
Author: Kroon, RE; Seed Ahmed, HAA; Gusowski, MA
Abstract: Silica is a basic material of technological importance for optics, microelectronics, photonics and fibre optics and it has been used as a host material for a variety of luminescent lanthanide ions due to its chemical stability and non - hygroscopic nature. Although f or lanthanide ions the 4f electron energy levels are shielded from the host environment by the filled outer 5s and 5p orbitals, making the f - f transitions relatively insensitive to the host , f - d transitions involving the unshielded 5d state are host dependent. The absolute positions of the 4f and 5d states relative to the valence and conduction bands of the host also affect quenching and charge trapping phenomena and so they are required for proper modelling of phosphor performance. Recently a model has been formulated to determine the ene rgy levels of any of the thirteen divalent lanthanides relative to the band edges using only three host dependent parameters. Another two host dependent parameters are required to also establish the absolute levels of the trivalent ions. In this paper a s cheme for the energy levels of both the divalent and trivalent lanthanide ions in silica is proposed making use of experimental data. It is suggested that although the location of the divalent europium ion f - level above the valence band can be located by using the charge transfer energy of triva lent europium, this process cannot be generalized to find the location of the trivalent cerium ion f - level above the valence band using the charge transfer energy of tetravalent cerium as has been suggested
URI: http://khartoumspace.uofk.edu/123456789/23462
Date: 2016


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