1. Gross,E.F.: Nuovo Cimento Suppl. 3, 672 (1956): — Advan. Phys. Sci. Moscow. 63, 575 (1957).
2. Nikitine,S.: J. Chim. Phys. 55, 621 (1958); — Phil. Mag. 4, 1 (1959); — J. Phys. Chem. Solids 8, 190(1959).
3. Nikitine,S.: Progr. Semiconductors 6, 235 (1962). See also, Optical Properties of Solids, p. 197. New York: Plenum Press 1969. In these two publications some bibliography can be found.
4. Knox,R.S.: Theory of Excitons, Solid State Phys. Suppl. 5 (1963); Academic Press.
5. Dexter,D.L., Knox,R.S.: Excitons. New York: J. Wiley 1965.