The term ``sensitized luminescence'' in crystalline phosphors refers to the phenomenon whereby an impurity (activator, or emitter) is enabled to luminesce upon the absorption of light in a different type of center (sensitizer, or absorber) and upon the subsequent radiationless transfer of energy from the sensitizer to the activator The resonance theory of Forster, which involves only allowed transitions, is extended to include transfer by means of forbidden transitions which, it is concluded, are responsible for the transfer in all inorganic systems yet investigated The transfer mechanisms of importance are, in order of decreasing strength, the overlapping of the electric dipole fields of the sensitizer and the activator, the overlapping of the dipole field of the sensitizer with the quadrupole field of the activator, and exchange effects These mechanisms will give rise to ``sensitization'' of about 103−104, 102, and 30 lattice sites surrounding each sensitizer in typical systems The dependence of transfer efficiency upon sensitizer and activator concentrations and on temperature are discussed Application is made of the theory to experimental results on inorganic phosphors, and further experiments are suggested

A Theory of Sensitized Luminescence in Solids

In Weiterentwicklung fruherer Theorien von J. und F. Perrin und klassischphysikalischer Uberlegungen des Verfassers wird eine quantenmechanische Behandlung des Ubergangs von Elektronenanregungsenergie zwischen gleichartigen Molekulen in Losung gegeben. Der kritische Molekulabstand, unterhalb dessen der ubergang wahrend der Anregungsdauer stattfindet, last sich aus den Absorptions- und Fluoreszenzspektren und der Anregungsdauer der Molekule berechnen. Fur Fluorescein und Chlorophyll a ergeben sich Werte von 50 bzw. 80 AE, entsprechend den mittleren Molekulabstanden in Losungen von 3,2 · 10−3 bzw. 7,7 · 10−4 Molen/Liter. Fur die Bereiche oberhalb und unterhalb der kritischen Konzentration werden Formeln zur Berechnung der Energieabwanderung vom Primarmolekul angegeben, die mit den vorliegenden Messungen der Konzentrationsdepolarisation der Fluoreszenz gut ubereinstimmen. Die Anwendung auf analoge Energiewanderungsprobleme in Molekulkristallen und im Assimilationsapparat der Pflanze wird diskutiert.

Zwischenmolekulare Energiewanderung und Fluoreszenz

It is rigorously proved that at any nonzero temperature, a one- or two-dimensional isotropic spin-$S$ Heisenberg model with finite-range exchange interaction can be neither ferromagnetic nor antiferromagnetic. The method of proof is capable of excluding a variety of types of ordering in one and two dimensions.

Absence of Ferromagnetism or Antiferromagnetism in One- or Two-Dimensional Isotropic Heisenberg Models

For centuries knowledge meant proven knowledge — proven either by the power of the intellect or by the evidence of the senses. Wisdom and intellectual integrity demanded that one must desist from unproven utterances and minimize, even in thought, the gap between speculation and established knowledge. The proving power of the intellect or the senses was questioned by the sceptics more than two thousand years ago; but they were browbeaten into confusion by the glory of Newtonian physics. Einstein’s results again turned the tables and now very few philosophers or scientists still think that scientific knowledge is, or can be, proven knowledge. But few realize that with this the whole classical structure of intellectual values falls in ruins and has to be replaced: one cannot simply water down the ideal of proven truth - as some logical empiricists do — to the ideal of’probable truth’1 or — as some sociologists of knowledge do — to ‘truth by [changing] consensus’.2

Falsification and the Methodology of Scientific Research Programmes

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

1. Crystal lattices. General theory 2. . Crystal lattices. Applications 3. Interaction of light with non-conducting crystals 4. Electrons in a perfect lattice 5. Cohesive forces in metals 6. Transport phenomena 7. Magnetic properties of metals 8. Ferromagnetism 9. Interaction of light with electrons in solids 10. Semi-conductors and luminescence 11. Superconductivity

Quantum theory of solids

Calculations are made of the size of a dislocation and of the critical shear stress for its motion.

https://iopscience.iop.org/article/10.1088/0959-5309/52/1/305/pdf

The size of a dislocation

Es wird untersucht, wann sich in der Quantenstatistik die freie Energie ohne Kenntnis der stationaren Zustande des Systems berechnen last. Mit den hierbei entwickelten Methoden wird die diamagnetische Suszeptibilitat von freien Elektronen, ihre Beeinflussung durch die Zusammenstose und das magnetische Verhalten gebundener Elektronen untersucht. Es wird festgestellt, bis zu welchen Feldstarken die Suszeptibilitat feldunabhangig ist.

Zur Theorie des Diamagnetismus von Leitungselektronen

Ising discussed the following model of a ferromagnetic body: Assume N elementary magnets of moment μ to be arranged in a regular lattice; each of them is supposed to have only two possible orientations, which we call positive and negative. Assume further that there is an interaction energy U for each pair of neighbouring magnets of opposite direction. Further, there is an external magnetic field of magnitude H such as to produce an additional energy of − μH (+ μH) for each magnet with positive (negative) direction.

Rudolf Peierls

Papers

Quantum theory of solids

The size of a dislocation

Zur Theorie des Diamagnetismus von Leitungselektronen

On Ising's model of ferromagnetism

Zur kinetischen Theorie der Wärmeleitung in Kristallen