1. Kolomiets, B.T. and Nazarova, T.F., Fiz. Tverd. Tela, 1959, vol. 2, p. 21.
2. Askhabov, A.M. and Sultanov, S.B., J. Optoelectron. Adv. Mater., 2003, vol. 5, no. 5, p. 1231.
3. Kolomiets, B.T. and Mamontova, T.N., J. Non-Cryst. Solids, 1972, vol. 8, no. 10, p. 1004.
4. Babaev, A.A., Mamontova, T.N., and Terukov, E.I., Fiz. Khim. Stekla, 1992, vol. 8, no. 5, p. 135.
5. Babaev, A.A., Kamilov, I.K., Sultanov, S.B., Askhabov, A.M., and Terukov, E.I., Inorg. Mater., 2005, vol. 41, no. 7, p. 771.