[1] Beall G H and Pinckney L R 1999 J. Am. Ceram. Soc. 82 5

[2] Pinckney L R 1999 J. Non-Cryst. Solids 255 171

[3] Samson B N et al 2002 Opt. Lett.
27 1309

[4] Reisfeld R et al 1984 Chem. Phys.
Lett. 104 153

[5] Buch A et al 1985 Mater. Sci. Eng.
71 383

[6] Reisfeld R 1985 Mater. Sci. Eng. 71 375

[7] Andrews L J, Beall G H and Lempicki A 1986 J. Lumin. 36
65

[8] Suzuki T and Ohishi Y 2004 Appl. Phys. Lett. 84 3804

[9] Suzuki T, Murugan G S and Ohishi Y 2005 Appl. Phys. Lett.
86 131903

[10] Suzuki T, Horibuchi K and Ohishi Y 2005 J. Non-Cryst.
Solids 351 2304

[11] Zhou S F, Feng G F et al 2006 Chin. Phys. Lett. 23
2996

[12] Schreyer W and Schairer J F 1962 Am. Mineral. 47 90

[13] Galoisy L and Galas G 1993 Geochim. Cosmochim. Acta 57
3613

[14] Reisfeld R, Kisilev A, Buch A et al 1987 J. Non-Cryst.
Solids 91 333

[15] Tanabe Y and Sugano S 1954 J. Phys. Soc. Jpn. 9 753,
766

[16] Kuleshov N V et al 1997 J. Lumin. 71 265

[17] Albers P, Stark E and Park S H 1985 J. Opt. Soc. Am. B
3 134