1. V. M. Agranovich, Theory of Excitons [in Russian] (Nauka, Moscow, 1969).
2. V. M. Agranovich and O. A. Dubovsky, Optical Properties of Mixed Crystals (North-Holland, Amsterdam, 1988), p. 297.
3. V. M. Agranovich and O. A. Dubovskii, JETP Lett. 26, 488 (1977).
4. V. M. Agranovich and O. A. Dubovskii, Fiz. Tverd. Tela (Leningrad) 20, 3237 (1978) [Sov. Phys. Solid State 20, 1867 (1978)].
5. Ya. B. Zel’dovich, Zh. Éksp. Teor. Fiz. 67, 2357 (1974) [Sov. Phys. JETP 40, 1170 (1975)].