1. J. T. Randall, Trans. Faraday Soc.,35, 2, 1939.
2. F. A. Kröger, Some Aspects of the Luminescence of Solids, Elsevier Publishing Co., London, p. 107, 1948.
3. N. Ryll, Luminescence [Russian translation], p. 38, Gostekhizdat, Moscow-Leningrad, 1946.
4. A. V. Moskvin, Cathodoluminescence, Part 2 [in Russian], p. 444, Gostekhizdat. Moscow-Leningrad, 1949.
5. A. M. Gurvich and R. V. Katomina, Novosti meditsinskoi tekhniki. VNIMIO, 3, 40.