The　absorption　and　the　emission　spectra　of　GaN　and　(Ga,AE)N　(AE　=　Be,　Mg,　Ca)　were　calculated　by　using　TDDFT　method　with　cluster　model.　The　calculation　results　show　that　Ga(26)N(2)GH(50)　cluster　only　has　very　weak　absorption　but　has　some　emission　bands　in　visible　region.　The　band-to-band　emission　appears　around　3.56　eV.　If　alkaline-earth　atoms　(Be,　Mg　and　Ca)　are　doped　into　GaN,　the　blue　emission　band　around　3.0　eV　appears.　Thereinto,　Ga25Ca1N26H50　cluster　shows　a　weaker　yellow　emission　band　and　a　stronger　blue　one　(2.92　eV),　which　make　(Ga,Ca)N　material　a　promising　candidate　to　emit　blue　light.　(c)　2009　Elsevier　B.V.　All　rights　reserved.