1. W. LEVERENZ, ?An Introduction to Luminescence of Solids? (Wiley, New York, 1950).
2. S. SHIONOYA, in ?Luminescence of Inorganic Solids?, edited by P. Goldberg (Academic, New York, 1966) p. 205.
3. D. CURIE and J. S. PRENER, in ?Physics and Chemistry of II?VI Compounds?, edited by M. Aven and J. S. Prener (North-Holland, Amsterdam, 1967) p. 434.
4. W. LEHMAN,J. Electrochem. Soc. 110 (1963) 754.
5. Idem, ibid.113 (1966) 788.