Electro- and photo-luminescent quenching effects imposed by field-induced ionization of the Eu2+ luminescent centers in CaS:Eu thin films

It is found that both the high-field electroluminescent (EL) and photoluminescent intensities of CaS:Eu thin films were quenched by an applied electric field. This quenching was found to be caused by a field-induced ionization of impact-excited Eu2+ luminescent centers. This ionization was known to play an important role in the memory and slow response characteristics of CaS:Eu thin-film electroluminescent devices. Evidence for field-induced ionization of Eu2+ was obtained from the following measurements of CaS:Eu; (i) the first and second EL emission peaks, (ii) photoluminescence, and (iii) photocapacitance.