A light-emitting device is provided that is excellent in light emission efficiency and stability. The light-emitting device has a first part of a first dielectric constant, a second part of a second dielectric constant and a third part of a third dielectric constant, and has a triple junction where they are in contact with one another. Moreover, a first and a second electrode are provided for applying a voltage for controlling an electric field at the triple junction and in the vicinity thereof. Further, at least one of the first, the second and the third parts is a constituted by light-emitting material, and the triple junction forms a closed line.