THIN-FILM ELECTROLUMINESCENT DEVICES USING CAS AND SRS

Recent advances in the development of thin-film electroluminescent (EL) devices having alkaline-earth sulfide phosphors doped with rare-earth luminescent centers are summarized. The effect of the preparation conditions on the quality of the resultant thin films is discussed. It is shown that the crystallinity of the evaporated thin films can be improved by an increase in substrate temperature, and that oxygen contamination is reduced by sulfur coevaporation. The EL characteristics and the excitation mechanism of these EL devices are discussed on the basis of the band structure of the alkaline-earth sulfides and the energy levels of the luminescent centers. Experimental results on the excitation spectra of photo-induced transferred charge, which give clear evidence for the ionization of the luminescent centers, are presented. The EL characteristics of white EL devices based on novel SrS phosphors are also discussed. © 1989.