Rare-Earth Excitation Mechanism in Wide Band Gap H-VI Compounds
K. Karpińska, K. Świątek, M. Godlewski
Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa, Poland

L. Niinistö
Laboratory of Inorganic and Analytical Chemistry, Helsinki University of Technology, 02150 Espoo, Finland

and M. Leskelä
Department of Chemistry, University of Helsinki, 00100 Helsinki, Finland
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The excitation mechanism of rare-earth emission in Eu and Ce doped CaS and SrS is studied. It is proposed that the Eu and probably also Ce emission is induced by the photoionization transition of the rare-earth ion, which is followed by the carrier trapping via the excited state of the ion. At increased temperatures the efficiency of excitation is reduced. We explain this effect by the carrier emission from the excited core state of the rare-earth ion to the continuum of the conduction (valence) band states. It is also suggested that the charge transfer state of the rare-earth ion may act as the intermediate state in the carrier trapping.
DOI: 10.12693/APhysPolA.84.959
PACS numbers: 71.55.Gs, 76.30.Kg, 78.55.Et