1. P. Pringsheim..Fluorescence and Phosphorescence, Interscience Publishers Ltd., London, 1949, 619.
2. —————.. Ibid., 1949, 620.
3. Milton and Hofstadter..Phys. Rev., 1949,75, 1289.
4. Unpublished data of Bonanomi and Rossel quoted by B. Hahn and J. Rossel,Helv. Phys. Acta, 1953,26, 276.
5. Electronics and Waves Monographs;J. B. Birks,1953