1. A. N. Winchell and H. Winchell, The Microscopical Characters of Artificial Inorganic Solid Substances: Optical Properties of Artificial Minerals, 3rd ed. (Academic Press, New York, 1964; Mir, Moscow, 1967).
2. G. Browmik, Indian J. Phys. 43, 43 (1960).
3. P. G. Hodgeson, J. Whitnalls, C. H. Kennar, and F. H. Moor, Struct. Commun. 4, 713 (1975).
4. L. V. Soboleva, Neorg. Mater. 31, 614 (1995).
5. C. J. Ballhausen, Introduction to Ligand Field Theory (McGraw-Hill, New York, 1962; Mir, Moscow, 1964).