1. F. Bloch, Z. Physik, 52:555 (1928).
2. É. I. Adirovich, Some Problems in the Theory of Luminescence of Crystals [in Russian], Gostekhizdat, 1956.
3. N. B. Hannay (ed.), Semiconductors, 1959.
4. T. O. Woodruff, Solid State Physics, Vol. 4 (1957).
5. F. Herman, Phys. Rev., 93:1214 (1954).