1. V. I. Al’shits, E. V. Darinskaya, T. M. Perekalina, and A. A. Urusovskaya, Sov. Phys. Solid State 29(2), 265 (1987).
2. N. N. Peschanskaya, V. Yu. Surovova, and P. N. Yakushev, Sov. Phys. Solid State 34(7), 1127 (1992).
3. Yu. I. Golovin and R. B. Morgunov, Phys. Solid State 37(7), 1152 (1995).
4. Yu. I. Golovin, Phys. Solid State 46(5), 789 (2004).
5. N. N. Peschanskaya and A. B. Sinani, Phys. Solid State 50(1), 182 (2008).