Highly efficient electroluminescence in sapphire and magnesia

Electroluminescence (EL) has been obtained and studied in two different wide band gap oxide crystals: MgO:Li (7.8 eV) and Al2O3:Mg (8.8 eV). EL requires crystal doping with Li or Mg to induce p-type conductivity and the formation of F-type centers which are the deep levels within the band gap for electron-hole recombination. Oxidizing treatments are required in Al2O3:Mg to reach adequate conductivities. The main EL emissions are at 2.35 eV (528 nm) for MgO:Li crystals and at 3.8 eV (327 nm) for Al2O3:Mg. Trace impurities also produce EL in the visible region, their control may be used for color designed LEDs.