BIBLIOGRAPHY

MAURICE CURIE, Luminescence des corps solides. Paris 1934, p. 144.
Maurice Curie, Luminescence of Solids.

The number of monographs devoted to questions of luminescence is very limited, while the need for such books is great. This is evidenced by the rapidly increasing number of original works on luminescence and the systematic increase in the circle of persons working in this field with theoretical or applied aims. Therefore one must regard as a very welcome phenomenon the forthcoming publication in France of a whole series of books devoted to questions of luminescence. Curie’s book is the first of them. The title of the book is not entirely precise: the whole book is devoted exclusively to the luminescence of inorganic phosphors (Lenard phosphors) and does not at all touch upon the question of the luminescence of pure crystals and solid solutions of organic dyes. The book is divided into 5 unequal chapters: photoluminescence, cathodoluminescence, radio- and radiophotoluminescence, triboluminescence, and scintillation and luminescence in flames.

If one compares this book with the well-known monograph of Pringsheim (Peter Pringsheim, Fluoreszenz und Phosphoreszenz, Berlin 1928), the completely different style of the two books at once strikes the eye. Whereas Pringsheim has a clear point of view on the fundamental processes of luminescence and leaves the reader, who is not sophisticated in these questions, unintentionally hypnotized by his sequential exposition, which gives rise to no obscurities, Maurice Curie, on the contrary, often has no clear point of view on one question or another. For the most part he merely conscientiously sets forth the existing theories and accompanies them with a number of critical remarks, referring here to his published and unpublished experiments. But he does not oppose the theory he criticizes with any other, more or less formulated one.

Such a style of Curie’s book is to a significant degree dictated by the very logic of things. At the moment of writing his book Pringsheim had at his disposal less theoretical and experimental material than Curie. The weak points of the existing theories had not yet been revealed with complete clarity. At the present time we have at our disposal already considerably more experimental material, and this material, as Curie shows, does not fit within the framework of the old theories and cannot always be easily understood from the standpoint of the new ones. This concerns first of all the very mechanism of excitation and emission. The mechanism of absorption is represented quite simply from the standpoint of Lenard’s theory of active centers, but this theory does not agree with a number of experimental facts and should be regarded only as a very visual scheme for describing the processes of luminescence.

On the other hand, the theory proposed by Saha that absorption for the case, for example, of $\mathrm{Cr}^{+++}$ consists in the removal of one of the $d$ electrons, although it gives, as Dèjardin has shown, a successful interpretation of the spectra of ruby, is still in an embryonic state and cannot yet give any more or less satisfactory explanation of a whole series of experimental facts. Curie himself supports rather the photoelectric

Bibliography

…ical theory of fluorescence and attempts, very plausibly, to connect it with Shah’s theory. Namely, Curie assumes that upon recombination the electron returns not directly to the luminogenic atom, but to an ionized atom of the solvent that is part of the luminogenic complex, and that the energy released in this recombination goes to the second kind of excitation of the luminogenic atom. Similar views had been expressed earlier by Tomaschek. The indicated hypothesis makes understandable the experimental fact that one and the same luminogenic center, as calculation shows, can emit, when the phosphor is excited, from 2 to 4 quanta with one and the same emission spectrum.

However, even such a combined scheme of the emission process still does not seem to us sufficiently convincing in view of a number of experimental data. A way out of the difficulty, apparently, can be found only if one makes use of the images of wave mechanics. An outline of such a theory was recently given by Blokhintsev.

All that has been said relates mainly to the chapter on photoluminescence, which occupies 100 pages in Curie’s book. The remaining chapters, indicated above, seem less interesting. There the author gives almost none of his own considerations, but confines himself to an exposition of the material existing on the given questions. Nevertheless, these chapters too are presented very vividly and written in a light style.

The book is designed quite satisfactorily and is supplied with a bibliography up to 1934.

B. Sveshnikov