Blue light-emission from a single-layer organic LED (light-emitting diode) based on carbazole dimers is reported. The device fabrication, involving vacuum sublimation of the dimer onto an indium tin oxide covered glass substrate, is described and the source of the electroluminescence elucidated. It is deduced that confined intra-dimer luminescence excitations and a balanced double-charge injection result in a device with good luminance and modest external quantum efficiencies. Of the three primary colors required for full-color display applications, blue has been the most elusive to obtain.