Nano- and microcrystalline Lu2O3:Eu phosphors: variations in occupancy of C2and S6sites by Eu3+ions

The occupancy of C-2 and S-6 sites by Eu3+, ions in nanocrystalline powders and microcrystalline ceramics of Lu2O3 prepared from these powders was studied by Mossbauer spectroscopy. It was proved that in nanopowders prepared by vigorous combustion syntheses the occupancy of the C-2 and S-6 sites by Eu3+, is almost random, with only a very limited preference for the former. For ceramic specimens formed at 1750 degrees C within a few hours, it was found that Eu3+ ions strongly prefer to enter the Lu2O3 host at the C-2 site. We concluded that thermodynamically the non-centrosymmetric site C-2 is preferred to the S-6 site by Eu3+. However, if the formation of crystallites is very fast, like in combustion syntheses, the Eu3+ ions are entrapped into the two sites nearly randomly.