[1] Zhang J C and Wang Y H 2008 Chin. Phys. Lett.
25 1453

[2] Li P L, Wang Z J, Yang Z P and Guo Q L 2009 Chin.
Phys. Lett. 26 047801

[3] Liang X L, Zhu C F, Yang Y X, Yuan S L and Chen G R 2008
J. Lumin. 128 1162

[4] Xiu Z L, Yang Z S, L\"{U M K, Liu S W, Zhang H P and Zhou
G J 2006 Opt. Mater. 29 431

[5] Su X Q and Yan B 2005 Mater. Chem. Phys. 93
552

[6] Wang Y H, Wu C F and Wei J 2007 J. Lumin. 126
503

[7] Li Y and Hong G 2005 J. Lumin. 26 587

[8] J\"{ustel T, Krupa J C and Wiechert D U 2001 J.
Lumin. 93 179

[9] Saito S, Wada K and Onaka R 1974 J. Phys. Soc. Jpn.
37 711

[10] Nakazawa E and Shiga F 1977 J. Lumin. 15 225

[11] Wu C F and Wang Y H 2008 Electrochem. Solid-State
Lett. 11 J9

[12] Dorenbos P 2000 J. Lumin. 91 91

[13] Yang H C, Li C Y, He H, Tao Y, Xu J H and Su Q 2006
J. Lumin. 118 61

[14] Su Q, Liang H B, Li C Y, He H, Lu Y H, Li J and Tao Y
2007 J. Lumin. 122--123 927

[15] He H, Liang H B, Wang S B, Su Q, Tao Y, Ju X and Hou X Y
2002 Nucl. Tech. 25 783

[16] Zhang J P, Liang H B, Han B, Tian Z F and Su Q 2008
Opt. Express 16 7508

[17] Li Y C, Chang Y H, Lin Y F, Chang Y S and Lin Y J 2007
J. Alloys Compounds 439 367

[18] Bao A, Yang H, Tao C Y, Zhang Y and Han L L 2006 J.
Lumin. 128 60

[19] Chen L M, Liu G C, Liu Y N and Huang K L 2008 J.
Mater. Proc. Technol. 198 129

[20] Mini K K, Anoop G and Jayaraj M K 2007 J.
Electrochem. Soc. 154 J310