Abstract
The luminescence of Eu 2+ in several silicate host lattices has been studied. In these structures there are chains of alkaline earth ions. In some cases the Eu 2+ ion in these chains shows emission at long wavelengths. This effect is due to preferential orientation of a d-orbital. In (Ca, Sr) 2MgSi 2O 7:Eu 2+ it is shown that if the cell parameters are increased by replacing (part of) the calcium by strontium ions, the effect of preferential orientation of a d-orbital in the chain direction decreases and the Eu 2+ emission shifts to shorter wavelengths. However, in SrSiO 3:Eu 2+ and CaSiO 3:Eu 2+ the chains of alkaline earth ions are close to each other and a blue Eu 2+ emission is observed. This indicates that preferential orientation of only one d-orbital is required to obtain a Eu 2+ emission at low energy. Finally, in BaSiO 3:Eu 2+, BaSi 2O 5:Eu 2+ and Sr 2LiSiO 4F:Eu 2+, where there is a network of alkaline earth ions through the lattice, the conduction band is lowered and an impurity-trapped exciton emission is observed. This situation is similar to that in BaF 2:Eu 2+.
Published Version
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