White-emission from ZnS:Eu incorporated in AC-driven electroluminescent devices via ultrasonic spray pyrolysis

Abstract

In this work, white-emitting-alternating-current-thin film electroluminescent (w-ACTFEL) devices are demonstrated using europium-doped zinc sulfide (ZnS:Eu) and zirconium oxide (ZrO2) as the emissive and dielectric layers, respectively. These films were deposited by the ultrasonic spray pyrolysis technique on antimony-doped tin oxide glass substrates, forming a standard metal-insulator-semiconductor-insulator-metal (MISIM) architecture. 10 kHz sinusoidal voltages activated the white-EL of the devices. The colorimetric characteristics were investigated for three amplitudes of the applied voltage. The emission of the devices is made up of wide and narrow bands with peaks corresponding to violet, blue, green and red light, which together produce the resulting white light. According to the colorimetric analysis, this white light is close to the standard D65 CIE illuminant with a minimal dominant blue component. The variation in voltage amplitude induces small changes in the visual characteristics of the EL emission. The white-EL emission of these MISIM devices is attributed to the electron-impact excitation and subsequent relaxation of the excited levels of Eu2+ and Eu3+ impurities, and defect levels in the sublayer regions adjacent to the ZrO2–ZnS:Eu interfaces.