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Cerium Containing Chalcogenides with Chromatic Properties
Published online by Cambridge University Press: 15 February 2011
Abstract
λ–Ce2S3, like many other cerium containing chalcogenides, presents a strong absorption in the visible spectra in relation with the CeIII-4fl → CeIII-5d1 electronic transition taking place at around 1.9 eV. This transition energy, that induces a red hue for the phase, can be increased by changing the nature of the Ce-S bonding, in particular through an enhancement of its ionicity. This can be made by inserting/substituting some alkali metal ions in the structure of λ-Ce2S3. The sodium-doped λ-Na3/8Ce15/2S3 phase for instance undergoes a CeIII-4f1 → Cemi-5d1 transition energy increase of 0.12 eV. This shift is sufficient to modify substantially the pigment properties of the material and it has been mainly related to the narrowing of the electronic bands. In CePS4, Ce2SiS5, Ce4Si3S12and Ce6Si4S17, strong covalent bondings enhance the ionic Ce-S bond through inductive effect, leading to a CeIII-4f1 → CeIII-5d1 electronic transition in the blue (Eg - 2.5 eV) hence the yellow hue of these materials. Within the Ce-Si-S family, small differences may be attributed to difference in the [CeSx] and [SiS4] polyhedra bonding. The Ce3(TS4 )2X family (X = Cl, Br, I, T = Si, Ge) does not show pigment properties because of the Ce-X bond inducing a more Ce-S ionic character (in particular when X = Br, I) and thus a higher gap that is found in the near ultraviolet. On the other hand, the phases present an important room temperature blue fluorescence.
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- Copyright © Materials Research Society 1999
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