[1] Tang C W,Van Slyke S A.Appl.Phys.Lett.,1987,51:913.

[2] Tang C W,Van Slyke S A,Chen C H.J.Appl.Phys.,1989,65:3610.

[3] Cao Y,Parker I D,Yu G.Nature,1999,397:414.

[4] Chuen C H,Tao Y T.Appl.Phys.Lett.,2002,81:4499.

[7] Kido J,Shionota H,Nagai K.Appl.Phys.Lett.,1995,67:2281.

[8] Jiang X Y,Zhang Z L,Zhang B X,et al.Synth.Met.,2002,129:9.

[10] Hao J G,Deng Z B,Yang S Y.Displays,2006,27:108.

[11] Yang S Y,Jiang Y,Teng F,et al.Solid State Commun.,2006,139:415.

[12] Cao J,Liu X,Khan M A,et al.Current Applied Physics,2007,7:300.

[13] Kim Y,Im W B.Physica Status Solidi(a),2004,201:2148.

[14] Cheng G,Zhao Y,Li F,et al.Thin Solid Films,2003,467:231.

[16] Yang S Y,Liu D,Jiang Y,et al.J.Lumin.,2007,122-123: 614.

[17] Deshpande R S,Bulovic V,Forrest S R.Appl.Phys.Lett.,1999,75:888.

[18] Burrows P E,Shen Z,Bulovic V,et al.J.Appl.Phys.,1996,79:7991.

[19] Shigeki N,Hiroyuki O,Hiroyoshi O,et al.Synth.Met.,2000,111-112:331