PHOTOINDUCED TRANSFERRED CHARGE IN RARE-EARTH-DOPED ALKALINE-EARTH SULFIDE ELECTROLUMINESCENT THIN-FILMS

The spectral response of the photo-induced transferred charge in Eu2+- or Ce3+-doped CaS and SrS thin-film electroluminescent (EL) devices has been studied. It is found that excitation spectra of the photo-induced transferred charge agree with those of photoluminescence. This result implies that the Eu2+ or Ce3+ luminescent centers are ionized by electric field when the centers are excited to the (4f)n-1(5d) excited state. The dynamics of the EL emission are controlled by field-dependent ionization of the luminescent centers and by field-dependent trapping at the ionized centers, rather than by impact excitation of the luminescent centers.