1. V. S. Vavilov, A. A. Klyukanov, K. D. Sushkevich, M. V. Chukichev, A. Z. Awawdeh, and R. R. Rezvanov, Fiz. Tverd. Tela (St. Petersburg) 41(7), 1176 (1999) [Phys. Solid State 41 (7), 1070 (1999)].
2. V. S. Vavilov, A. A. Klyukanov, K. D. Sushkevich, M. V. Chukichev, A. Z. Awawdeh, and R. R. Rezvanov, Fiz. Tverd. Tela (St. Petersburg) 43(5), 776 (2001) [Phys. Solid State 43 (5), 808 (2001)].
3. A. A. Klyukanov, K. D. Sushkevich, M. V. Chukichev, and V. Gurau, Fiz. Tverd. Tela (St. Petersburg) 46(10), 1746 (2004) [Phys. Solid State 46 (10), 1805 (2004)].
4. V. M. Agranovich, Theory of Excitons (Nauka, Moscow, 1968) [in Russian].
5. Y. Toyozawa, Prog. Theor. Phys. 27(1), 89 (1962).