1. Williams R. T.: Semiconductors and Insulators3 (1978) 251.
2. Lushchik Ch. B.: “Excitons”, (ed. by E. I. Rashba and M. D. Sturge), North-Holland, 1981 (in press).
3. Toyozawa Y.: Vacuum Ultraviolet Radiation Physics, (ed. by E. E. Koch, R. Haensel, C. Kunz), Pergamon-Vieweg, Braunschweig, 1974, p. 317.
4. Williams R. T., Bradford J. N., Faust W. L.: Phys. Rev. B18 (1978) 7038.
5. Stoneham A. M.: Adv. Phys.28 (1979) 457.