The present invention relates to electroluminescent devices employing single-ion conductors as the materials for an electron- or hole-injecting layer. Preferred electroluminescent devices employ an electron- or hole-injecting layer made of single-ion conductors in a conventional electroluminescent device which comprises: a transparent substrate; a semitransparent electrode deposited on the transparent substrate; a hole-injecting layer positioned on the semitransparent electrode; an electroluminescent layer made of organic luminescent material, positioned on the hole-injecting layer; an electron-injecting layer positioned on the electroluminescent layer; and, a metal electrode deposited on the electron-injecting layer. The electroluminescent devices of the invention have excellent electroluminescent efficiency and low turn-on voltage, which make possible their application to the development of high efficiency electroluminescent devices.