Chronicle

Second All-Union Conference on Luminescence

From May 17 to 22, 1948, the Second All-Union Conference on Luminescence and the Application of Phosphors, convened by the Commission on Luminescence under the Division of Physical and Mathematical Sciences of the USSR Academy of Sciences, took place in Moscow. The Conference summed up the results of work in the field of luminescence carried out in the period since the first conference, held in October 1944.

The unabated interest in questions of luminescence on the part of physicists, chemists, lighting engineers, geologists, biologists, and representatives of other specialties shows the great scientific and practical significance of this area of optics.

Opening the Conference, Academician S. I. Vavilov outlined the historical course of the development of the doctrine of luminescence. Beginning with a description of individual “curious” phenomena that amazed investigators by their unusual character, it has grown into an orderly science, most closely connected with the rest of physics, becoming an integral part of the doctrine of the structure of atoms, molecules, and crystals and determining the entire character of modern optics. The history of the development of the field of luminescence is an excellent illustration of the fruitful influence of practice upon theory. For a number of centuries no serious attempts were made to create a theory of the phenomenon, despite the fact that such names as Boyle, Newton, Lomonosov, Euler, Boscovich, Petrov, Arago, Brewster, Stokes, Becquerel, Lommel, and many others appear in the history of luminescence. There were either only isolated successful attempts to explain individual phenomena. Internal ordering of the doctrine was hindered, on the one hand, by the absence of the absolutely necessary “nonclassical” concepts of quantum physics and of the doctrine of the structure of matter and, on the other hand, by the complete detachment of luminescence from the practical demands of technology, which deprived this field of knowledge of the powerful, persistent influence of the practical factor. Undoubtedly, if the practical significance of luminescence had been realized earlier than it actually was, the paths of development of all physics might have been entirely different, since the paths toward the discovery of the quantum features of natural phenomena in the field of luminescence are simpler and more direct. The chief and fundamental lesson that can be drawn from the centuries-long history of luminescence consists, as S. I. Vavilov indicated, in the necessity and extreme importance of strengthening the connection between theory and practice.

It was under the sign of this closest unity of theory and practice that all the work of the Conference proceeded; alongside profound theoretical investigations, reports were presented on works of important applied significance.

At 11 sessions of the Conference, 39 papers were read, devoted to various questions of the theory of luminescence and its practical appli-

...opinion. The main sections of the Conference’s program were: 1. Luminescence and the structure of molecules. 2. Luminescence of crystallophosphors and glasses. 3. Methods for the investigation of luminescence. 4. Luminescent analysis. 5. Luminescent light sources and their application. 6. Application of phosphors.

1. At the first session of the Conference two major reports were heard, by Academician A. N. Terenin and Academician S. I. Vavilov, concerning questions of the energetics of complex organic luminescent molecules.

A. N. Terenin, in his report “Quenching of photoluminescence and metastable states,” described the results of experimental work carried out in his laboratory by A. V. Karyakin. A. V. Karyakin quantitatively investigated the quenching by oxygen of the fluorescence of anthraquinone and its derivatives in vapors and in the adsorbed state. It was established that fluorescence is quenched by oxygen only in the case when the maximum of the fluorescence spectrum is located at wavelengths shorter than 500 mµ. If, however, the wavelength at the maximum exceeds 530 mµ, the fluorescence is not quenched either in vapors or in adsorbates. In particular, it was established that β-substituted compounds (OH, NH₂, CH₃) with fluorescence maxima at \(\lambda < 500\) mµ are quenched, whereas α- and polysubstituted compounds with a longer-wave spectrum (\(\lambda > 530\) mµ) are not quenched at all. In 1943 A. N. Terenin proposed a hypothesis on the mechanism of quenching by oxygen, according to which quenching occurs in the case when the energy difference between the excited and metastable levels of the fluorescing molecule, lying at a depth of \(\sim 1.5\) eV, is sufficient to transfer an \(O_2\) molecule from the triplet to the singlet state. To confirm this hypothesis with new data, an attempt was undertaken to find, in the compounds investigated, a metastable level at a depth of \(\sim 1.5\) eV. This attempt was successful. The discovery of phosphorescence in the infrared part of the spectrum made it possible to give a scheme of the energy equations of molecules of anthraquinone derivatives and confirmed the proposed hypothesis.

The report by S. I. Vavilov (made by him on his own behalf and on behalf of M. D. Galanin and F. M. Pekerman), “An experimental investigation of the migration of excitation energy in fluorescent solutions,” was devoted to an interesting and important question of intermolecular exchange of excitation energy. As is known, with increasing concentration of the fluorescing substance in a solution, the yield of luminescence, its degree of polarization, and the lifetime of the molecule in the excited state decrease. Several years ago S. I. Vavilov developed a general theory of all three phenomena, proceeding from ideas about the existence between excited and unexcited molecules of a peculiar inductive resonance, as a result of which the excitation energy can pass from one molecule to another. At the time this theory was compared with all known experimental data; however, these data were largely accidental, and a systematic joint study of all three phenomena had not been undertaken. In recent years all three phenomena have been subjected to a new, thorough, and systematic investigation in the works of M. D. Galanin and F. M. Pekerman, and the experimental results obtained fully confirmed the correctness both of the theory as a whole and of its individual conclusions. In the course of the investigation it proved possible to establish certain new regularities which, it may be hoped, will in the future make it possible to refine the mechanism of inductive interaction. Thus, for example, it proved possible to establish a phenomenological connection between the possibility of inductive resonance and the spectral characteristics of luminescence. A necessary condition for the development of all three phenomena associated with increasing concentration proved to be the presence of a more or less...

of a considerable overlap of the spectral bands of emission and absorption. S. I. Vavilov emphasized in his report that ideas about the resonant transfer of excitation energy, which entered the theory of luminescence through quantum mechanics, are in fact already contained in classical physics, although until now they had not been considered in it. Inductive resonance and the energy migration that is its consequence must manifest themselves not only in phenomena of luminescence. It is possible that a number of phenomena in the fields of photochemistry, biophysics, and other areas of science are connected with inductive resonance.

1. In the section devoted to questions of the connection between the structure of organic molecules and their luminescent properties, which had been absent from the program of the 1st Conference, 4 reports were read, showing that in the study of these fundamental and at the same time very little investigated questions, Soviet researchers had achieved definite successes.

In the report by P. P. Feofilov, “Polarization of luminescence and the structure of molecules,” the principal characteristics of polarized luminescence were considered; it was shown that polarization diagrams, i.e., diagrams indicating the spatial distribution of the polarization of luminescence, make it possible to establish (in most cases unambiguously) the nature of elementary emitters—their multipolarity, and that polarization spectra, i.e., curves expressing the dependence of the observed polarization on the wavelength of the exciting light, make it possible to establish the relative arrangement of the elementary oscillators of the molecule that determine the emission and absorption of light of various wavelengths, and that, finally, the study of the limiting values of polarization, i.e., of the values observed when all known depolarizing factors have been eliminated, makes it possible to express definite judgments concerning the symmetry of the molecular structure. Considering from this point of view a number of examples, the speaker sought to show that the study of the polarization of luminescence may be a new method for investigating the structure of molecules.

The report by V. V. Zelinskii concerned the principal problem of luminescence—the connection between fluorescence and the structure of organic molecules. The speaker pointed out that the existing experimental material had not in its time been treated sufficiently critically, and moreover that its treatment had become outdated, as a result of which a number of authors developed doubts as to the value of this material itself. However, an analysis of all the available experimental data shows that the basic regularities established by the older authors can be retained, although they do require modernization. The problem is reduced to finding the causes that produce quenching of fluorescence—the transformation of electronic energy acquired upon excitation into the vibrational energy of the molecule. Functional groups entering into the composition of the molecule may be divided into two classes: 1) groups possessing a great affinity for electrons; the negative end of the molecular dipole falls on them; these groups act in a quenching manner (diminophoric groups); 2) groups possessing little affinity for electrons; the positive end of the dipole usually falls on them; in a number of cases these groups also weaken fluorescence. In the process of absorption of light, the character of the bond of negatively charged groups changes, which leads to an internal conversion of the energy of electronic excitation into vibrational energy—to quenching. The speaker illustrated these propositions with a number of examples, examining also more complex cases of several “active” substituents. Considering the homologous series of phthalimides he had studied, as well as literature data on other series of compounds, V. V. Zelinskii proposed that the different action of substituents for different mutual arrangements of them—

may be connected with the linear character of the oscillators determining the absorption and emission of light.

The fruitfulness of studying homologous series of compounds was also demonstrated in the report by N. D. Zhevandrov, V. L. Lëvshin, and K. K. Mozgova, “On the influence of structure on the optical properties of 9–10-dihydroanthracene derivatives,” read by V. L. Lëvshin. In this work the influence of the nature and position of substituents introduced into the side chain of the compound on the optical properties of the molecules was studied (absorption and luminescence spectra, light yield, duration of excited states). The influence of the nature of the substituents proved stronger than the influence of their position. The compounds studied luminesce both in solutions and in the crystalline state, which made it possible to compare their optical properties in different aggregate states. The duration of the excited state in crystals proved to be of the order of several units of \(10^{-9}\) sec. The great duration of luminescence in crystals and the large light yield indicate a comparatively weak interaction of the molecules in the crystalline state. A very strong, though not regular, influence of the aggregate state on the spectral characteristics was discovered. A comparison of the duration of the excited states and the luminescence yield of various compounds of the series studied made it possible to establish a qualitative parallelism between these quantities; the most brightly luminescing compounds have the longest duration of excited states.

The report by B. Ya. Sveshnikov was devoted to the phosphorescence of organic compounds, observed when molecules are introduced into a solid medium or when they are adsorbed on the surface of various media. Starting from the Jablonski scheme, which assumes that molecules have a metastable level with a somewhat lower energy than the energy of the excited molecule, the speaker considered the kinetics of transition processes between the normal, excited, and metastable levels and showed that the transition from the excited state to the metastable one takes place during the entire time the molecules remain in the excited state. The question of the nature of metastable levels cannot be regarded as settled; the most widely accepted at present is the Lewis–Terenin hypothesis, according to which metastable states correspond to the triplet (biradical) state of the molecule. A study of the dependence of the duration of phosphorescence on the viscosity of the medium, carried out in binary mixtures of various solvents (not causing quenching), showed that the duration is a function of viscosity alone. The speaker noted in conclusion the interest presented by the study of metastable states, which are a necessary link in a number of chemical reactions.

1. A central place on the agenda of the Conference was occupied by questions of the theory of phosphorescence and solids. The lively discussion of all the reports in this section testified to the great interest in these complex and topical questions, the investigation of which is essential not only for the science of luminescence but also for the construction of the modern theory of the solid state.

V. L. Lëvshin delivered a report on behalf of four authors—V. V. Antonov-Romanovsky, V. L. Lëvshin, Z. L. Morgenshtern, and Z. A. Trapeznikova—“Interaction of activators in the mechanism of luminescence in flash phosphors.”

On the basis of a comprehensive investigation of phosphors possessing the property of emitting accumulated light energy under the action of long-wavelength light, the authors succeeded in elucidating the character of the interaction of the activators of these phosphors—two rare-earth elements—whose simultaneous presence in the phosphor leads to the development of flash capability. Study of the temperature glow curves of one- and two-activator

of phosphors has shown that the curves of two-activator phosphors cannot be obtained additively from the curves of the corresponding one-activator phosphors, which indicates the appearance in two-activator phosphors of special levels of electron localization connected with the formation in the phosphor of interacting groups of different activators. In the study of the spectral composition of the emission at the moment of excitation it was found that the introduction of a second activator not only changes the intensity of the emission of the first—samarium—but even leads to the appearance of new lines in its spectrum, which testifies to the existence of a very strong interaction of activators in the phosphor. The difference between the emission spectra at the moment of excitation of the phosphorescence, of thermic and of optical bleaching points to differences in the mechanism of these processes. A study of the temperature properties of optical bleaching showed that for it some thermal excitation of the electron with energy of the order of 500 cal is necessary. The course of optical bleaching as a function of the wavelength of the bleaching rays was investigated in detail for phosphors with one and with two activators. On the basis of the entire body of experimental data, the authors come to the conclusion that in two-activator phosphors there exist stable chemical formations of the type of complexes between two activators.

As V. V. Antonov-Romanovskii showed in his report “On the bleaching action of exciting light,” a number of experimental data relating to a broad group of phosphors of different classes serve as direct proof that exciting light also possesses a bleaching (sometimes quenching) action, as a result of which the limiting concentration of the stored light sum is a function of the wavelength of the exciting light. The presence of this dependence suggests that the energy of the absorbed quantum can be transferred not only to electrons located in luminescence (excitation) centers, but also to electrons localized in some places of the lattice (bleaching). The spectral region of the bleaching action overlaps the spectral region of excitation; therefore exciting light of any wavelength may have a greater or lesser bleaching action. The speaker showed that the insufficient ability of a phosphor to accumulate the light sum cannot be explained by the limited concentration of local levels, since the spectral dependence of the bleaching action remains unclear in that case.

The report by E. I. Adirovich, “Band theory of crystal phosphors and the phenomenon of the cold flash,” was heard with great interest. Considering band theory as the basis of modern statements about the luminescence of crystal phosphors, the speaker pointed out the necessity of giving a precise formulation to the boundaries of applicability of this theory. The processes of luminescence of crystal phosphors should be considered as a combination of optical processes (which take place in luminescence centers) and semiconductor processes (which are played out throughout the entire crystal). Only the latter belong to the competence of band theory. The kinetics of phosphorescence is determined by these same processes. The band model made it possible to explain the unusually great duration of afterglow and to obtain a law of attenuation satisfactorily agreeing with experiment. However, to explain temperature dependences an additional complication of the model is necessary. In particular, one may introduce ideas about a thermal barrier at the levels of excited centers. These ideas enabled the speaker to predict a peculiar phenomenon, “the cold flash,” subsequently discovered experimentally. The cold flash is a luminescence observed upon strong cooling of a phosphor which had previously been excited and then had bleached at room temperature. A number of experiments proved that the observed luminescence is not connected with triboluminescence, which might have been caused by destruction of the crystals upon abrupt cooling—

tions. For a quantitative explanation of the cold flash it is necessary to assume the existence of small local levels of adhesion. This assumption can be justified experimentally.

From other points of view, the report of V. M. Kudryavtsev, “On the interaction of electronic transitions with thermal vibrations in a crystal lattice,” approaches questions of the mechanism of photoluminescence of solids. The author considers the absorption spectra and low-temperature fluorescence of crystalline zinc sulfide and zinc oxide, and shows that both spectra have an electron-vibrational character. The peculiar temperature radiation of ZnS and ZnO is easily explained when the absorption spectra of these substances are considered on the basis of Kirchhoff’s law.

In the work of F. I. Vergunas, the dependence of the intensity of the spontaneous afterglow of certain crystal phosphors on the excitation intensity was investigated. Temperature quenching of the spontaneous afterglow can be described by the formula

$$ I=\frac{I_0}{1+C\cdot e^{-\frac{u}{km}}}, $$

where the coefficient \(C\) increases with decreasing excitation intensity \(E\) according to the law

$$ C_i=\frac{C}{E_i^m} $$

(the index \(i\) indicates a decrease of \(E\) by a factor of \(i\)). Thus, the absence of a linear relation between \(I\) and \(E\) can be explained by the dependence of \(C\) on \(E\), i.e., it can be connected with the presence of temperature quenching. Experiments carried out with the phosphors ZnS·Zn, ZnO, and others showed that

$$ C\sim \frac{1}{\sqrt{E}}, $$

and also that, in agreement with theoretical expectations, the dependence of \(I\) on \(E\) is linear at low temperatures; at high temperatures \(I\) decreases faster than in proportion to \(E\).

The practically important questions of the decay of luminescence under cathode excitation were considered in the report of A. V. Moskvin. In a number of cases the decay curve can be divided into three stages: two exponential ones with durations of \(\sim 10^{-6}\) and \(10^{-3}\), and a longer hyperbolic one. These stages are expressed differently in different luminophores, and they may be regarded as reflecting parallel processes.

The luminescence of ZnS·Cu under excitation by \(\alpha\)-rays (radioluminescence) was investigated in the work of T. V. Timofeeva. An important result of this work was the establishment of proportionality between the brightness of scintillations and the volume of the crystal up to certain limiting crystal dimensions (\(d\sim 5\mu\)). With further increase in size, the brightness of the scintillation remains constant. This indicates that, up to certain dimensions, the ZnS·Cu crystal is excited as a whole. In the work, the light yield under excitation by \(\alpha\)-rays was also studied. The obtained value of the yield (2–4.5%) agrees with the data of a number of earlier investigations and contradicts the data recently obtained by Riehl.

The report of F. D. Klement was devoted to clarifying the nature of infrared quenching in phosphors. Presenting extensive experimental material obtained with CaS·Pb and ZnS·Cu phosphors, the speaker showed that, despite the substantially different mechanism of luminescence of these phosphors, infrared quenching in both cases is connected with the presence in the conduction band of additional electrons—above the number corresponding to the number of positive holes formed in the ground band. An increase in the number of electrons in the conduction band leads to an increase in the number of radiationless transitions, i.e., to quenching.

The reports by M. L. Kats and I. A. Parfianovich concerned the luminescence of scheelite-like crystals containing centers of color. The relative simplicity of the structure of these phosphors and the specific nature of their behavior on heating—the presence of several distinctly expressed maxima on the thermoluminescence curve—make it possible to construct a sufficiently reliable scheme of energy levels, assigning individual levels to one or another formation in the crystal lattice.

In his report “Luminescent Properties of Crystallophosphors and Their Chemical Structure,” M. A. Konstantinova-Shlezinger pointed to the necessity of taking into account, along with the energy characteristics of phosphors, their crystal-chemical structure. The speaker considers the basis of the activation process to be complex formation—the formation in the field of certain bonds of the activator atom with the basic lattice. Diffusion of the activator is a necessary, but by no means sufficient, condition. The study of chemical bonds in crystallophosphors should indicate the path toward the rational production of luminous compositions.

In the report “On Certain Properties of ZnS, ZnS—CdS and ZnS—Se Luminophors and the Influence on Them of Chemical Treatment,” A. A. Bundel showed that the activators of zinc sulfide, in addition to the generally known Ag, Cu, Mn and Zn, may also be Fe, Ni, Co, and also Cd at small concentrations. Study of the dependence of luminescence on the nature of the chemical treatments used in preparing the luminophor shows that such activators as Ag, Cu, Mn, Fe, and Co are present in the free state. The speaker indicated that the activators of zinc sulfide may be not only metals but also metalloids (for example selenium).

A. N. Sevchenko described a number of new and interesting phenomena discovered in the study of the luminescence of uranium salts and glasses. He established the specific character of the dependence of the degree of polarization of the luminescence of uranium glasses on the wavelength of the exciting light. The form of this dependence proved to be highly sensitive to small changes in the composition of the glass. The degree of polarization of the luminescence drops sharply as the latter decays, which agrees with the theory of concentration phenomena developed by S. I. Vavilov. The emission spectrum of certain glasses changes as the luminescence decays, acquiring a more sharply expressed structure. In addition to the usual emission of the uranyl ion, lasting \(10^{-4}\) sec., emission of glasses and crystals observed at the temperature of liquid air and lasting several seconds was discovered and studied. By a series of carefully arranged experiments the speaker showed that, contrary to statements made earlier, crystals of uranyl compounds can luminesce even in the complete absence of water of crystallization.

T. I. Weinberg spoke about the research she had carried out on the luminescence of glasses containing copper, lead, and samarium. In copper glasses an intense long-lasting afterglow was found, allowing the conclusion that crystalline formations are present in the glass.

4. A special session was devoted to questions of the methodology of luminescence research.

In the report by N. A. Tolstoy and P. P. Feofilov, an automatic oscillographic method for studying the processes of flare-up and decay of luminophors occurring in the time interval \(10^{-5}\)—\(10^{-1}\) sec. was presented. The method is based on periodic excitation of luminescence by rectangular light (or any other) pulses, photoelectric recording of the emission, and the sweep of the flare-up and decay curves on the screen of a cathode-ray oscilloscope, taking place according to an exponential law with an arbitrarily and continuously varying exponent parameter \((\tau)\). If the process under study is exponential, then, by choosing the sweep parameter equal to

for the desired parameter (the criterion is the straightening of the curve on the screen), one can immediately find the latter. A slight complication of the method makes it possible to extend it also to non-exponential processes. The speed of measurements and the high accuracy of the results obtained make it possible to use the new technique for studying the influence on the character of the flare-up and decay of various factors (temperature, intensity of the exciting light, external fields, etc.).

The instrument constructed on the basis of this technique (the “taumeter”) was demonstrated at the exhibition opened during the Conference.

E. M. Brumberg and F. M. Pekerman reported on a new method for studying the absorption spectra of crystallophosphors. As is known, the main obstacle in studying the absorption of fine-crystalline powders is the strong scattering of light. Using a spectral attachment (with quartz optics) on an ultraviolet microscope, E. M. Brumberg managed to obtain absorption spectra for individual microcrystals of phosphors. The use of immersion made it possible to weaken to a considerable extent the influence of scattered light.

E. K. Putseiko spoke about the application of the condenser method to the study of the photoelectric sensitivity of dyes and phosphors. The condenser method is based on recording the appearance of photoelectrons released inside a substance by measuring the capacitance of a condenser filled with the substance under investigation. Using this method, it proved possible to determine the photoelectric sensitivity of the phosphors ZnO and ZnS; moreover, an approximate coincidence was established between the region of photoelectric sensitivity and the region of intrinsic absorption. The method also makes it possible to determine the sign of the current carrier—the character of the conductivity (electronic, hole, mixed).

M. N. Meisel spoke about the methods and possibilities of luminescence microscopy in a large report, “Some Results and Prospects for the Application of Luminescence Microscopy in Biology.” The speaker indicated that in a number of cases an apparatus for luminescence microscopy can be implemented quite simply—with the use, for excitation, of short-wave visible (blue) light. The possibility of increasing the intensity of the exciting source is limited by photochemical processes; therefore, in order to increase sensitivity it is advisable to use more sharply contrasting fluorochromes, to increase the yield of luminescence, and to reduce light losses in the optics of the microscope.

A new opak-illuminator for the luminescence microscope, developed by E. M. Brumberg and S. A. Gershgorin and based on the use of interference light filters, proved extraordinarily effective for the purposes of luminescence microscopy.

On the basis of extensive investigations carried out by the speaker and his collaborators, it was established that fluorochroming of living objects and subsequent luminescence-microscopic examination make it possible, in a number of cases, to reveal fine cellular structures, their physicochemical features, and also the initial stages of functional and pathological changes in cells. Especially significant results were obtained with the aid of the luminescent microscope in studying the processes of degeneration and death of living organisms, the mechanism of action of bactericidal and antibiotic substances. Luminescence microscopy has made accessible the study of the entry, movements, and transformations of certain vitamins and tumor-producing substances in the organism and within individual cells.

1. The problems of macroscopic luminescence analysis were addressed in the survey report of M. A. Konstantinova-Shlezinger and in a number of reports on specific applications of luminescence analysis to various particular problems.

Luminescence analysis, as M. A. Konstantinova-Shlezinger noted in her report, has undergone considerable evolution in recent years, with growth observed both in breadth and in depth. There are fields in which luminescence analysis has already fully justified itself. Thus, for example, it is widely used in the search for useful minerals (especially petroleum, where an entire branch of luminescent bituminology is developing), in defectoscopy, in the sorting of optical glass, etc. New fields of application are arising (for example, forensic chemistry). Alongside this, work is being carried out to find new methods and techniques; new additional characteristics of luminescence are being brought into use (spectra, duration of afterglow, dependence on temperature, quenching, etc.). The development of analysis in depth encounters certain fundamental difficulties, in particular insufficient clarification of the phenomenon of quenching and of the question of the possibility of “paralyzing” the action of the quencher. The broad application of luminescence analysis is still greatly hindered by a lack of apparatus.

The use, for the purposes of luminescence analysis, of phosphoroscopic observations and short-wave ultraviolet excitation made it possible for E. M. Brumberg, Z. M. Sverdlov, and T. V. Timofeeva to develop a luminescence method for sorting optical glass, which makes it possible to identify a considerable portion of the glasses from the rich assortment produced by industry.

On the necessity of making use, in the luminescence analysis of minerals, of the physical characteristics of the glow, G. F. Komovskii spoke in his report. As such characteristics the speaker indicated: 1) color of the glow, 2) its intensity, 3) spectrum, 4) glow under cathodic excitation, 5) glow under ultraviolet irradiation, 6) fluorescence, 7) phosphorescence. The principal characteristic nevertheless appears to be the spectrum of the glow, which is sufficient, and sometimes very characteristic, for a number of minerals.

A. F. Fioletov, in a report on the luminescence analysis of bitumens, noted that at present the luminescence method is the principal method for investigating the bituminousness of rocks and waters.

A communication by M. M. Laushkina was devoted to the application of luminescence in defectoscopy.

1. A number of reports were devoted to luminescent lamps as one of the principal technical applications of luminescence. On the state of production of luminescent lamps, R. A. Nilender spoke in his report. In the report of D. A. Shklover, the spectral and color characteristics of the radiation of luminescent lamps were presented, and methods for their control were set forth.

Problems of the physics of luminescent lamps were investigated in the work of F. A. Butaeva and V. A. Fabrikant. Of extraordinary interest are the data obtained in the work, indicating that, when luminophores are excited by the second resonance line of the mercury discharge \((\lambda = 1850\ \text{Å})\), the yield of luminescence is almost twice the yield under excitation by light with wavelength \(2537\ \text{Å}\).

Several reports were devoted to questions of the operation of luminescent lamps. Special investigations showed the effectiveness of using luminescent light sources for growing plants under artificial light; the favorable influence of new light sources on vision was established, etc. On the major work on luminescent illumination of the exhibition halls of the Ermi-

also reported by D. N. Lazarev. The need for luminescent lamps is very great, and it cannot be satisfied by the comparatively small quantity that is being produced at the present time.

7. The application of luminous compositions in various areas of life is extraordinarily diverse, and at the Conference only certain individual questions could be considered. Z. M. Gorev shared his experience in the practical use of luminous compositions, describing new types of luminescent illuminators for scales of various instruments and methods for protecting phosphors from atmospheric effects.

The reports by E. M. Mandelberg and I. V. Gorbachev on the application of luminescence in the visual arts and in architecture, accompanied by impressive demonstrations, were heard with great interest.

The Conference showed that extensive, varied, and productive work is continuing in the field of the study and application of luminescence. In the years that have passed since the first Conference, several of the most important problems of luminescence concerning the luminescence of molecules and crystals have been solved, and new original research methods have been developed. Along with the former ones, luminescence has acquired new important applications for lighting-engineering and analytical purposes. The Conference showed that Soviet specialists in luminescence, who constitute, as Acad. S. I. Vavilov noted in summing up the Conference, an indisputably very strong detachment of present-day science, are successfully carrying out the task set before all our science—to catch up with and surpass the achievements of foreign science.

P. Feofilov