Thin-film electroluminescent emitters based on calcium sulfide doped with cerium

Abstract

Thin-film electroluminescent structures (TFELS) based on calcium sulfide doped with cerium have long evoked interest, especially in recent years. Such systems feature a higher quantum yield compared with traditional zinc-sulfide doped with manganese due to the screened state of the shells within which radiative transitions take place. The CaS-Ce luminophor does not have a great tendency toward saturation, in contrast ZnS-Mn, which seems to be attributable to the similar chemical properties of the cations of the basic type AIIa and ions of rare-earth elements of type AIIIa. Moreover, their ionic difference is small. The band gap of calcium sulfide is equal to 3.4-4.4 eV, which permits one to apply an electric field of the high strength necessary for exciting electroluminescence. However, in their durability and electroluminescence yield these structures are three-four times inferior to zinc-sulfide systems. In our opinion, such a short TFELS lifetime is explained by a lack of understanding of the mechanisms involved in current passage and electroluminescence in the literature. Proceeding from these prerequisites, in the present work we carried out investigations of the voltage-current (VCC) and voltage-brightness (VBC) characteristics of CaS-Ce.