Abstract: Electrochemical light emitting devices are disclosed which include a composite material in contact with two electrodes. The composite material is an admixture of ionic species and an `immobile` semiconductor. The semiconductor is capable of supporting both p- and n-type carriers and having a doping profile which can be dynamically changed in a controlled fashion through reversible electrochemical oxidation and reduction. Devices having this structure may be used to generate electrochemically induced p-n junctions, thereby providing a new means of exploiting the light emitting properties of such junctions under an applied voltage. Systems and methods for generating useful levels of light employing these devices are also disclosed.