1. A. B. Lyskovich (ed.). Wide-Gap Layered Crystals and Their Physical Properties [in Russian], Vishcha Shkola, L'vov (1982).
2. I. V. Kityk, Zh. Prikl. Spektrosk.,43, No. 3, 487?489 (1985).
3. Ya. O. Dovgii and I. V. Kityk, Ukr. Fiz. Zh.,29, No. 6, 884?889 (1984).
4. S. Kondo and H. Matsumoto, J. Phys. Soc. Jpn.,51, No. 5, 1441?1448 (1982).
5. G. B. Bachelet, D. R. Haman, and M. Schlüter, Phys. Rev. B,26, No. 8, 4199?4227 (1982).