1. J. Pankove, in: Processes in Semiconductors, Prentice-Hall, Englewood Cliffs, NJ, 1971, p. 456.
2. F. Bassani, G.P. Parravichini, in: Electronic States and Optical Transitions in Solids, Pergamon Press, Oxford, 1975, p. 391.
3. E.D. Aluker, D.Yu. Lusis., S.A. Chernov, in: Electronic Excitations and Radioluminescence of Alkali-Halide Crystals, Zinatne, Riga, 1979, p. 251 (in Russian).