Large increases in the efficiency of the Sr2SiO4:Eu yellow phosphor under the 450-470 nm excitation range have been achieved by adding the co-doping element (Ba2+ and Mg2+) in the host. In order to apply to white light-emitting diodes (LEDs), we have synthesized a Ba(2+)center dot Mg2+ co-doped Sr2SiO4: Eu yellow phosphor and investigated an attempt to develop white LEDs by combining it with an InGaN blue LED chip (460 nm). Two distinct emission bands from the InGaN-based LED and the Ba2+center dotMg2+ co-doped Sr2SiO4: Eu phosphor are clearly observed at 460 and at 560 nm, respectively. These two emission bands combine to give a spectrum that appears white to the naked eye. (c) 2005 The Electrochemical Society. All rights reserved.