The mechanism of energy transfer from Si nanocrystals to Er ions in SiO2 - Different mechanisms depending on Er concentrationK. Imakita, M. Fujii and S. HayashiEur. Phys. J. D, 34 1-3 (2005) 161-163DOI: https://doi.org/10.1140/epjd/e2005-00137-2