1. “Verfärbung und Lumineszenz, Beiträge zur Mineralphysik”, 166 (Springer-Verlag, Wien, 1953). An interpretation, differing from mine, of the absorption spectra of fluorite has been given by Lüty, F. (Z. Phys., 134, 596; 1953), of Göttingen.
2. Smakula, A., Phys. Rev., 77, 408 (1950); “Verfärbung und Lumineszenz”, 168. It can be pointed out here that these artificial crystals still contain appreciable traces of rare earths, as follows from the coincidence of the maxima in the thermoluminescence spectra observed by Hill, J. J., and Aron, J. (J. Chem. Phys., 21, 223; 1953), with the well-known rare earth emission lines.
3. “Verfärbung und Lumineszenz”, 173.
4. “Verfärbung und Lumineszenz”, 188.
5. “Verfärbung und Lumineszenz”, 196.