Bibliography

G. F. J. Garlick, Luminescent materials. Oxford, 1949, p. 254; G. Garlick, Luminescent Substances.

The content of Garlick’s monograph and the very fact of its appearance are closely connected with the struggle of ideas that is now taking place in the theory of luminescence of crystallophosphors. The central point in this struggle is the kinetic scheme of electronic processes in luminescing crystals. This struggle arose as early as the pre-quantum period of the theory, when the classical bimolecular concepts of Wiedemann and Schmidt¹, owing to their inadequacy, gave way to Lenard’s monomolecular theory². In 1933–1936 V. V. Antonov-Romanovskii and V. L. Levshin³,⁴ gave direct experimental proof of the bimolecular nature of luminescent processes in crystallophosphors. On this experimental basis there arose and developed the modern bimolecular band theory of the luminescence of crystalline phosphors, proposed by I. I. Blokhintsev⁵. Against the bimolecular theory and its substantiation in the works of Soviet authors, Randall and Wilkins⁶, and also Garlick and Wilkins⁷, came out in 1945. E. I. Adirovich⁸ showed, however, that the “metastable” theory of Randall and Wilkins is erroneous. The fundamental error of Randall and Wilkins consists in neglecting repeated capture of electrons (retrapping) in the afterglow process. Proper allowance for this effect leads to radically different results. These results made it possible to interpret the experiment on the decay of crystallophosphors without resorting—as Randall and Wilkins do—to a wholly unproven summation of exponentials with specially chosen coefficients. The erroneousness of the theoretical concepts of Randall and Wilkins was subsequently noted by other authors as well⁹,¹⁰,¹¹,¹².

The broad criticism of the ideas of Randall, Wilkins, and Garlick, first advanced by Soviet and then by foreign authors, received no direct reply from them. In a series of papers published over the last five years by Garlick¹³,¹⁴ and others, the original erroneous ideas about the monomolecular nature of the mechanism of luminescence of crystallophosphors are repeated not only without any attempt to subject them to criticism, but even without any mention of the works in which proof of the erroneousness of these ideas was given. Meanwhile, consideration of the recent publications of the Randall school shows that the conception of Randall, Wilkins, and Garlick has evolved in a definite way toward a gradual elimination from it of internal contradictions noted by criticism. This is especially clearly seen when comparing the main works of 1945⁶,⁷ with Garlick’s monograph under review, published in 1949.

The title of the book is broader than its actual content, which relates almost entirely to crystalline phosphors activated by metal impurities. The monograph consists of nine chapters and contains references to the literature (about 300 titles) up to 1948; it should be noted that the literature of recent years (1945–1948) is represented very incompletely and one-sidedly.

The first chapter of the monograph is devoted to clarifying: 1) the general conditions for the luminescent ability of bodies; 2) the structure of luminescence centers; 3) a survey of quantum theories. In the first question the author limits himself to a formal scheme for potential curves of Mott-Seitz. In the second—to a summary of experimental data that allow one to assert that luminescence centers of two types exist—molecular centers ($\mathrm{Mn}^{++}$, $\mathrm{UO}_2^{++}$, etc.), and more complex ones consisting of an activator ion ($\mathrm{Cu}$, $\mathrm{Zn}$, $\mathrm{Ag}$, etc.) and a group of lattice ions. We note that although much attention is given to luminescence centers in Garlick’s book, and although various speculative statements about the mechanism of luminescence of crystalline phosphors are connected with them, there are no concrete factual data on the constitution and structure of these centers in the monograph. The historical survey is extremely inaccurate. Thus, for example, the division of luminescence into monomolecular and bimolecular is attributed to E. Becquerel, whereas these kinetic concepts themselves were developed considerably later than the corresponding works of E. Becquerel. The basic and most important empirical formula of E. Becquerel, $U=(a+bt)^{-\alpha}$, established by him in 1860[^15], is attributed to some Hopkinson and Jesty, with a reference to an unpublished work of 1946 (!). As the first work on the band theory of crystal afterglow, Garlick cites Johnson’s paper (1939), whereas this theory was stated by L. I. Blochintsev[^5] as early as 1934.

The second chapter of Garlick’s book is devoted to presenting theoretical ideas about the mechanism of luminescence of crystalline phosphors. However, apart from general introductory information from the band theory of solids, the content of this chapter is erroneous. This main theoretical chapter of the book consists chiefly of a retelling of Randall and Wilkins’ ideas on the monomolecular kinetics of the luminescence of crystalline phosphors, the erroneousness of which was shown in its time in the works of E. I. Adirovich[^8] and V. V. Antonov-Romanovskii[^9]. Garlick, avoiding polemics with these results, simply does not mention them. Meanwhile not only the second chapter, but the entire book is devoted to a single task—to prove the admissibility of neglecting repeated sticking of electrons in the process of afterglow. Such tendentiousness makes the book uninteresting, since the whole selection of material is calculated not for a broad illumination of the problems considered, but for confirmation of the author’s erroneous main thesis. It is curious to note that, as one of his arguments, the author cites the work of Herman and Meyer of 1946,[^16] whereas these same authors, in a special note[^11], admitted the erroneousness of the neglect of repeated sticking of electrons which they had carried out following Randall and Wilkins, and in their 1948 article[^17], after two years of calculations with the aid of an electronic integrator, they arrive at the same results that E. I. Adirovich obtained in 1946.

In the third chapter a classification is given and each of the types of practically most interesting crystalline phosphors is considered. A small paragraph is devoted to “pure” phosphors, mainly diamond. The entire remaining part of the chapter is devoted to various phosphors activated by impurities.

In doing so, along with a description of the properties, optical characteristics, and technology of each of the phosphors, the author devotes considerable attention

...subjecting the curves of temperature glow to analysis, which is very typical of Randall’s school. However, the author does not give a correct interpretation of Zamenhof’s fact of the “deep” trapping levels (p. 54). Under prolonged excitation to saturation, electron capture by shallow trapping levels cannot suppress the storage of light sum at deep levels. The reason here is different—the necessity of activating the process of electron trapping, the activation energy being the greater, the deeper the level.^18

In the section devoted to alkali-halide phosphors, the author discusses the well-known experiments of Bunger and Flechsig (1931), which showed that the decay of certain KCl·Tl samples follows the exponential law: \(I = I_0 e^{-\alpha t}\), where \(\alpha = S e^{-\varepsilon/kT}\). This result, which served as the basis for notions of a metastable mechanism of luminescence in alkali-halide phosphors [Seitz (1938), Randall and Wilkins (1945), et al.], is interpreted by the author in the sense that V. V. Antonov-Romanovskii^19 had already earlier proved the bimolecular character of the luminescence of these compositions. Instead of considering the numerous experimental proofs of V. V. Antonov-Romanovskii that unambiguously decide this question, Garlick adduces the banal argument that the hyperbolic decay of KCl·Tl can be represented as a sum of exponentials. The allowance for the possibility of decomposing a hyperbola into exponentials, of course, in no way proves the reality of each such component or the monomolecularity of the process. Let us note that E. I. Adirovich^8,20 showed that the very result of Bunger and Flechsig follows directly from the bimolecular scheme of phosphor luminescence for sufficiently small effective trapping cross sections.

The fourth chapter is devoted to the consideration of: 1) the luminescence yield as a function of the experimental temperature and the excitation conditions; 2) the role of repeated electron trapping; 3) the nature and position in the lattice of luminescence centers and trapping sites.

On the first question Garlick cites literary and his own experimental data which are, on the whole, considerably less substantial than the results, published in 1946–1948, of V. A. Yastrebov, V. L. Levshin, F. I. Vergunas, and F. F. Gavrilov, not cited by the author. The theoretical illumination of quenching phenomena is based on the ideas of Schoen and Klassen, relating to the kinetics of excitation-energy migration, and leaves aside the problem of the mechanism by which it is transformed into heat at “quenching centers.”

The second section of this chapter is the central part of the book. Here the author sets himself the goal of proving the insignificance of repeated electron trapping. However, instead of the promised proof, the author gives only a few experimental curves of temperature glow, compared with theoretical curves obtained without allowance for and with allowance for repeated electron trapping. The results prove to be equally unconvincing, which is not surprising, since Garlick mistakenly believes that allowance for repeated trapping necessarily leads to a hyperbola of the second order. Having failed to achieve the desired aim, the author notes with regret that on the basis of these data no final conclusion can be drawn about the role of repeated electron trapping. He turns to the experimental decay curves of ZnS·Cu and Zn₂SiO₄ and establishes that they, as a rule, are expressed by a hyperbola with fractional exponents. Such a course of decay corresponds exactly to the bimolecular notions of the luminescence of crystal phosphors.^8 Not understanding this and proceeding from the erroneous conviction that a bimolecular mechanism corresponds to a hyperbola of the second order, Garlick regards the fact of decay according to

fractional hyperbola, as proof of the validity of the monomolecular concept they defend. The main argument consists in the fact that a fractional hyperbola can be represented as the sum of exponentials. Here Garlick repeats Lenard’s path and then exactly rewrites his ideas on isolated luminescence centers, within which all the processes take place: absorption, adhesion, thermal release, recombination. Garlick thereby also explains the absence of repeated adhesions of electrons. A comparison of this chapter with Lenard’s works^2 shows a touching coincidence of views and will be all the more useful because Garlick does not cite Lenard here. However, 40 years ago the chemical theory of Wiedemann and Schmidt did not contain direct proof of the bimolecularity of the mechanism of luminescence of crystalline phosphors and could not give an interpretation of the experimental data on decay described by Becquerel’s fractional hyperbola. Therefore Lenard’s argumentation was to some extent convincing. The modern bimolecular theory, however, rests on direct proof of bimolecularity, first given by V. V. Antonov-Romanovskii,^4 and also on a vast amount of experimental material indirectly confirming this theory. The modern bimolecular theory has received the fractional hyperbola of Becquerel as an elementary theoretical law of decay.^8,20 Therefore, pointing to the fact of the decay of phosphors according to the law of the fractional hyperbola as a decisive argument in favor of the monomolecular theory produces a strange impression and shows the author’s complete lack of any serious arguments.

In the fifth chapter the electrical properties of phosphors are considered: the change of electrical conductivity during luminescence; the change of dielectric permittivity and dielectric losses; “electrophotoluminescence,” excited by strong electric fields. On the basis of literary and his own experimental data, Garlick concludes that both changes in dielectric permittivity and changes in dielectric losses are due to adhesion electrons, and not to conduction electrons. In this way Garlick attempts to prove the validity of his basic ideas about the monomolecular mechanism of luminescence, i.e., that absorption, adhesion, and emission take place within individual centers. The experimental facts cited by Garlick testify precisely to the contrary. It is enough to point to Garlick’s own results, which show that the slope of the hyperbola of phosphorescence decay does not coincide with the slope of the hyperbola of the decay of light-sum in a phosphor (see Fig. 76), and no further confirmation of the bimolecularity of the luminescence process is to be expected. It is indicative that Garlick himself further admits the discrepancy of the facts with his views and, in order to save the latter, is forced to make additional and unfounded assumptions (pp. 137–139).

The last paragraph of the fifth chapter (“electrophotoluminescence”) is a brief summary of Destriau’s works (1937–1947) on the excitation of luminescence of phosphors by strong alternating electric fields.

In the sixth chapter phosphors sensitive to infrared light are considered: 1) alkali-halide sulfides activated by rare earths, and 2) zinc sulfides containing Mn, Pb, and Cu. The experimental material is given mainly according to the works of Urbach and his co-workers and Ward. The existence is noted of a luminescent and extinguishing effect of infrared light depending on the wavelength, as well as the significant role of one-

of the temporary presence in the phosphor of two activators. All these facts are well known to the Soviet reader from the works of V. L. Levshin, V. V. Antonov-Romanovskii, Z. L. Morgenshtern, and Z. A. Trapeznikova. The theoretical interpretation of the experiment on phosphors sensitive to infrared light is carried out within the scheme of Garlik’s general ideas about the monomolecular nature of luminescent processes taking place at individual luminescence centers. As yet another argument in favor of his point of view (more precisely, in favor of the ideas of Randall’s school), Garlik cites the result of Ellikson and Parker, who found that the decay of these phosphors caused by infrared light proceeds according to the law of a second-order parabola. For Ellikson and Parker, who correctly integrated the equations of electronic kinetics in phosphors, but then lost the principal solution and obtained a second-order hyperbola, such an experimental result gave rise to a search for an explanation in side effects (light absorption in a thin layer of the phosphor). Garlik recognizes the equivalence of such an interpretation with the ideas about the sum of exponentials and therefore concludes that the question of the mono- or bimolecular character of the luminescence of crystalline phosphors remains open (pp. 168–169). This is a very valuable admission after all Garlik’s widely advertised statements about the monomolecularity of luminescence and the absence of repeated electron sticking. It is also significant that here Garlik recognizes the decay experiment as a decisive criterion (crucial test) in the question of the mechanism of luminescence of crystalline phosphors. Meanwhile, as was shown by E. I. Adirovich,^8 in order to explain the results of Ellikson and Parker there is no need to resort to assumptions about side effects; these results agree exactly with the bimolecular theory of luminescence of crystalline phosphors. Consequently, the “decisive criterion” does not speak in favor of Garlik, who came out in defense of Randall’s ideas.

The seventh chapter is devoted to cathodoluminescence and consists mainly of a description of the properties of screen phosphors (zinc and calcium sulfides and silicates) and their behavior under various conditions of cathodic excitation. The reader will find much fuller information in the recently published two-volume monograph by A. V. Moskvin.^21 At the end of the chapter, general theoretical information is briefly presented on the interaction of an electron beam with matter and on the mechanism of cathodoluminescence. The author also fails here to reconcile the reported facts with monomolecular notions.

The eighth chapter (“Luminescence of Organic Molecules”) stands apart and is only weakly connected with the rest of the material of the book. It briefly presents general information on the luminescence of organic molecules in solutions and in the solid state (structure of spectra, quenching, polarization, depolarization, etc.). To a considerable extent, the material of this chapter relies on the works fundamental for this field by S. I. Vavilov and his collaborators. A small paragraph is devoted to the luminescence of polymerized dyes.

In the last, ninth, chapter of the book, a brief résumé of all that precedes is given.

On the whole, Garlik’s monograph is of no interest either to the specialist or to the unprepared reader. The factual information on luminescence and luminophores is presented in it very cursorily, hastily, and does not shine with novelty. The theoretical treatment of the phenomena is erroneous. A vast body of experimental and theoretical material, unambiguously proving the bimolecularity of the luminescence of crystalline phosphors, is simply ignored. As a result of its extreme tendentiousness in the attempt to defend the erroneous ideas of the school

Randall’s monograph by Garlick gives the reader completely incorrect notions about the mechanism of luminescence of crystals and about the state of actual experimental and theoretical knowledge in this field.

E. Adirovich

References Cited

1. E. Wiedemann and G. C. Schmidt, Ann. der Phys. 54, 604 (1895); 56, 201 (1895).
2. Hand. Exp. Phys., 23, vol. I and II, 1928.
3. V. L. Levshin and V. V. Antonov-Romanovskii, DAN SSSR, No. 5, 205 (1933); ZhETF, 4, 1022 (1934).
4. V. V. Antonov-Romanovskii, DAN SSSR 2 (11), 93 (1936); Trudy FIAN 1, issue 2, 35 (1937).
5. D. I. Blokhintsev, DAN SSSR 2, 76 (1934).
6. J. T. Randall and M. H. F. Wilkins, Proc. Roy. Soc. (A) 184, 347, 366, 390 (1945).
7. G. F. J. Garlick and M. H. F. Wilkins, Proc. Roy. Soc. (A) 184, 408 (1945).
8. E. I. Adirovich, DAN SSSR 53, 317 (1946); Izv. AN SSSR, ser. fizich. 10, 467 (1946); ZhETF 18, 58 (1948).
9. V. V. Antonov-Romanovskii, Izv. AN SSSR, ser. fizich. 10, 477 (1946).
10. H. A. Klasens and M. E. Wise, Nature, 158, 483 (1946).
11. R. C. Herman and C. F. Meyer, Journ. App. Phys. 18, 258 (1947).
12. D. Curie, Journ. de Phys. 11, 179 (1950); C. R. 230, 1400 (1950).
13. G. F. J. Garlick, Cornell Symposium of the American Physical Society, 1948; Reports on Progress in Physics 12, 34 (1949) (Physical Society of Great Britain).
14. G. F. J. Garlick and A. F. Gibson, Proc. Phys. Soc. 60, 574 (1948).
15. E. Becquerel, C. R. 51, 921 (1860).
16. R. C. Herman and C. F. Meyer, Journ. App. Phys., 17, 743 (1946).
17. R. C. Herman, C. F. Meyer and H. S. Hopfield, JOSA 38, 999 (1948).
18. E. I. Adirovich, Izv. AN SSSR, ser. fizich. 13, 101 (1948).
19. V. V. Antonov-Romanovskii, Trudy FIAN 2, issue 2–3, 157 (1942).
20. E. I. Adirovich, Trudy FIAN 5, 387 (1950).
21. A. V. Moskvin, Cathodoluminescence, vols. 1, 2, 1948–1949.