White-light emission from electroluminescence diode with polyaniline as the emitting layer

A light-emitting diode (LED) with emeraldine base polyaniline (PAn) as the emitting layer, indium-tin oxide coated glass plate as the hole injector and deposited aluminum (or magnesium) thin film as the electron injector was fabricated, which can emit nearly white light covering the full range of visible light (380-750 nm). It is found that the white light is emitted from the phase with reduced repeat units (amine form), while the phase with oxidized repeat units (quinoid form) has no contribution to the emitting light. The turn-on voltage for eye-observable light intensity is 13 and 6 V for the LEDs with aluminum and magnesium electrodes, respectively, at a thickness of the emitting layer of 800 Angstrom. The range of the electroluminescence (EL) spectrum covering the range 300-800 nm is much broader than that of the photoluminescence (PL) spectrum, 350-510 nm.