1. S. I. Pekar, Zh. Eksp. Teor. Fiz.,33, 1022 (1957).
2. V. M. Agranovich and V. L. Ginzburg, Crystal Optics with Allowance for Spatial Dispersion. Exciton Theory [in Russian], Nauka, Moscow (1979).
3. V. M. Agranovich, Zh. Eksp. Teor. Fiz.,37, 430 (1959).
4. V. M. Agranovich, Theory of Excitons [in Russian], Nauka, Moscow (1968).
5. E. Hanamura, J. Phys. Soc. Jpn.,37, 1545 (1974).