1. R. V. Pisarev, Ferroelectrics 162, 191 (1994).
2. V. N. Krivoruchko and D. A. Yablonskiĭ, Zh. Éksp. Teor. Fiz. 94(9), 268 (1988) [Sov. Phys. JETP 67 (9), 1886 (1988)].
3. V. N. Krivoruchko, T. N. Solov’eva, and D. A. Yablonskiĭ, Opt. Spektrosk. 68(4), 942 (1990) [Opt. Spectrosc. 68 (4), 550 (1990)].
4. V. N. Krivoruchko and T. E. Primak, Fiz. Tverd. Tela (Leningrad) 33(11), 3205 (1991) [Sov. Phys. Solid State 33 (11), 1810 (1990)].
5. V. N. Krivoruchko and T. E. Primak, Opt. Spektrosk. 88(1), 62 (2000) [Opt. Spectrosc. 88 (1), 55 (2000)].