1. A. V. Golubkov, E. I. Goncharova, V. P. Zhuze, G. M. Loginov, V. M. Sergeeva, and I. A. Smirnov, Physical Properties of Rare-Earth Chalcogenides (Nauka, Leningrad, 1973) [in Russian].
2. V. V. Kaminskii and Yu. M. Sosov, USSR Inventor’s Certificate No. 1554433 (1988).
3. L. N. Vasil’ev, V. V. Kaminskii, M. V. Romanova, N. V. Sharenkova, and A. V. Golubkov, Phys. Solid State 48, 1884 (2006).
4. S. I. Grebinskii, V. V. Kaminskii, A. V. Ryabov, and N. N. Stepanov, Sov. Phys. Solid State 24, 1069 (1982).
5. L. N. Vasil’ev, V. V. Kaminskii, Yu. M. Kurapov, M. V. Romanova, and N. V. Sharenkova, Phys. Solid State 38, 430 (1996).