An electroluminescent (EL) device is disclosed. An optically reflective concave structure includes a first surface and a second surface that lies at an angle relative to the first surface, wherein at least the first and second surfaces are optically reflective. One or more functional layers include a light emitting layer, disposed over the surfaces of the optically reflective concave structure, wherein at least one electroluminescent area of the light emitting layer is defined on the first surface. Especially, the ratio between the diameter of the first surface and the thickness of the one or more functional layers in the optically reflective concave structure is smaller than a constant value.