J. van Dijk

On the nonradiative and radiative decay rates and a modified exponential energy gap law for 4f–4f transitions in rare‐earth ions

A modified exponential energy gap law for nonradiative decay has been derived for 4f–4f transitions where only a few phonons participate in the transition. Its preexponential factor varies by only a factor of 10 for different host materials and is purely electronic in nature. The modified law is the usual law (giving a factor of 105 variation) modified by using an energy gap which is effectively two (maximum) phonon energies smaller than the energy difference between the initial and the final electronic state. A general relation between the radiative and nonradiative decay rates has been constructed. For 4f–4f transitions this relation enables one to predict the nonradiative decay rate from a knowledge of the radiative decay rate to within one order of magnitude accuracy.

On radiative and non-radiative decay times in the weak coupling limit

Abstract A modified exponential energy gap law for nonradiative decay has been derived for 4f-4f transitions where only a few phonons participate in the transition. Its preexponential factor varies by only a factor of 10 for different host materials and is purely electronic in nature. The modified law is the usual law (giving a factor of 10 5 variation) modified by using an energy gap which is effectively two (maximum) phonon energies smaller than the energy difference between the initial and the final electronic state. A general relation between the radiative and nonradiative decay rates has been constructed. For 4f-4f transitions this relation enables one to predict the nonradiative decay rate from a knowledge of the radiative decay rate to within one order of magnitude accuracy. The paper also contains a review of the theory of nonradiative and radiative decay in the presence of weak electron-phonon coupling and the Judd-Ofelt theory for forced electric dipole 4f-4f transitions.

The dissolution of Na2O-MgO-CaO-SiO2 glass in aqueous HF solutions

The dissolution (or etching) of a multicomponent (Na2O-MgO-CaO-SiO2) silicate glass in aqueous HF solutions is studied. The solutions were chosen in the systems HF-HNO3-H2O, HF-HCl-H2O and HF-H2SO4-H2O, and the temperatures varied from 25 to 60° C. SEM micrographs of the glass surface after etching show an “orange peel” surface structure which develops during etching and which originates from surface flaws. The dissolution rate of the glass was found to increase with higher HF concentration, higher strong-acid concentrations and higher temperatures. The dissolution rate is determined by the reaction of HF molecules and HF2 ions with the Si-O-Si grouping surrounding the SiO4 tetrahedron. In the multicomponent glass some of these bonds are non-bridging due to the presence of Na2O, CaO and MgO, increasing the dissolution rate significantly. H+ ions introduced by adding strong acids to the etch solution adsorb on the surface and catalyse the dissolution reaction. Several models used to describe the relation between the dissolution rate and the H+ concentration are discussed.

Derivation of the relation between non-radiative and radiative decay rates in rare-earth ions with comparison to experimental energy gap, parameters and the consequences for non-radiative selection rules

Abstract Experimentally the electronic coupling element for non-radiative decay in rare-earth ions has been derived from the energy gap law. We derive that the effective energy gap to be used in the energy gap law is about two phonons smaller than the energy difference between initial and final state. The effective electronic coupling element determined in this way from experiment varies little for all known solids and is in good agreement with our theoretical calculation of this parameter. Also we can predict exceptions to the energy gap law with our theory.

6 Non-Tricyclic Antidepressants

Publisher Summary This chapter discusses recent developments in “non-tricyclic antidepressants” and the test methods on which the conclusion of “probably therapeutically active” is based have been evaluated. The chapter discusses the activities of the various new structures, classified by structural resemblance. Some general structure-activity relations (SAR) are also discussed in the chapter. In general, the therapeutic properties of tricyclic antidepressant drugs are attributed to their inhibition of a transmitter uptake by monoaminergic neurons in the central nervous system. This hypothesis is based mainly on the pharmacological properties of these tricyclics in animal experiments viz. the antagonism of monoamine depleting agents, the potentiation of directly or indirectly acting amine agonists, and the decrease in amine uptake processes by appropriate cells or cell fragments. In the non-tricyclic antidepressant, structures there are promising drugs in which the side effects of the tricyclics are absent.

Über eine neue adrenalincarbonsäure und einige ihrer derivate

Abstract Synthesis and pharmacological properties of a new carboxylic acid of epinephrine and of some derivatives are reported. The carboxylic acid produced qualitatively the same effects on blood pressure and denervated nictitating membrane of the cat as epinephrine, the relative potency being 0.0003. The effects on the blood pressure could be reversed by previous administration of adrenalytics. We believe that the effects on the blood pressure and the nictitating membrane are caused by admixture of epinephrine contained in the original substance. An enzymatic decarboxylation in vitro could not be observed. On the other hand, the effects of the esters derived from the new epinephrine carboxylic acid were similar to those of the iso propylnorepinephrine. The most active ester derived from the new acid equalled iso propylnorepinephrine in its potency on all test subjects. In all experiments, the increasing effects on heart frequency, the bronchodilating and the depressing effect on the blood pressure of the esters run parallel. The corresponding derivatives of the p-oxyephedrin were practically completely ineffective. The connections between chemical constitution and pharmacological activity is discussed.

Mono- and polycrystalline silicon emitters for bipolar transistors grown by molecular beam epitaxy

Abstract Molecular beam epitaxial silicon was used to grow epitaxial and polysilicon emitters in self-aligned bipolar transistors with the “double poly” structure. The emitter characteristics of the transistors were compared with various types of polysilicon emitters grown by low pressure chemical vapour deposition. It is shown that the molecular beam epitaxial silicon emitter provides the lowest emitter series resistance and has an adequate emitter efficiency.

3-D effects in emitter-base junctions in advanced silicon bipolar transistors

Summary form only given. The authors report experimental results on double-polysilicon self-aligned n-p-n transistors that clearly indicate that the emitter-base reverse characteristics are inherently limited by three-dimensional effects in the corners of the emitter, and that two-dimensional considerations fail to explain many results for a large variety of experimental conditions. Without any exception it is found that the emitter-base reverse characteristics of narrow emitters (14*0.8 mu m/sup 2/) shown higher reverse leakage currents than large emitters (14*10 mu m/sup 2/), even when compared on an absolute scale. In addition it appears that a large walled emitter (i.e. with two sides overlapping the field oxide) tends to show far better reverse characteristics than a large nonwalled emitter with a common rectangular geometry. The difference in leakage current at a given reverse bias can be as high as two orders of magnitude. The results obtained can be explained qualitatively in terms of the three-dimensional concentration profiles of the boron under the oxide sidewall spacer in the corner of an emitter. >

Quantum Mechanical Calculation of the Relation Between the Radiationless and Radiative Decay Rates with Application to Molecules in the Gas Phase and Ions in the Solid State and the Consequences for Temperature Quenching (Abstract Only)

A general relation between the radiationless and radiative decay rates is derived, whereby we not only consider the vibrational overlap integrals for the two processes, but also the electronic factors that cause these processes. This proves possible, because the operators responsible for these processes, the electric dipole moment and the non-adiabatic Born-Oppenheimer coupling, turn out to be related to each other.