An energetic-electron emitter providing electrons having kinetic energies on the order of one thousand electron volts without acceleration through vacuum. An average electric field of 10.sup.5 V/m to 10.sup.10 V/m applied across a layer of emissive cathode material accelerates electrons inside the layer. The cathode material is a high-dielectric strength, rigid-structure, wide-bandgap semiconductors, especially type Ib diamond. A light-emitting device incorporates the energetic-electron emitter as a source of excitation to luminescence.