Electroluminescence is the creation of light by applying an electric bias to a material. It may employ AC or DC voltage. It is employed in LEDs and in large area displays etc.
When the applied forward voltage on the diode of the LED drives the electrons and holes into the active region between the n-type and p-type material, the energy can be converted into infrared or visible photons. This implies that the electron-hole pair drops into a more stable bound state, releasing energy on the order of electron volts by emission of a photon. The red extreme of the visible spectrum, 700 nm, requires an energy release of 1.77 eV to provide the quantum energy of the photon. At the other extreme, 400 nm in the violet, 3.1 eV is required.
See the IDTechEx report Introduction to Printed Electronics