Anomalous thermal quenching of luminescence in ZnS:Cu phosphor crystals

We studied the thermal quenching of luminescence (TQL) in the case of photoexcitation (PE, _e=313 and 365 nm) and cathodoexcitation (CE) with a high excitation density (10¹⁸ cm^–3· sec^–1) in ZnS:Cu single crystals with various degrees of copper supersaturation, EL-455 and K-83 copper-activated powders, and ZnSCu epitaxial thin films. Our study of TQL in the blue and green bands showed that two types of quenching anomalies are observed in the specimens used. An anomaly of the first type manifests itself in the fact that, with band-to-band excitation (_e = 313 nm and CE). the green band is quenched earlier than the blue band and small steps are observed on the quenching front. This anomaly is explained with the aid of a dislocation model of the blue center. An anomaly of the second type is observed in specimens not supersaturated with copper and consists of the quenching of luminescence beginning earlier at a high excitation (CE) density than at a low excitation (PE) density and proceeds in the same way in the blue and green bands. The thermal depths of the acceptors level are estimated from TQL for the three fundamental luminescence bands 440, 468, and 525 nm which are equal to 0.38 ±0.05, 0.7–0.8, and 0.9–1 eV, respectively.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–43, July, 1979.     

Development of P1-monodentate diamidophosphites with a C1-symmetric 1,2-diamine backbone: the effects of substituents in the 1,3,2-diazaphospholidine cycle on Pd-catalyzed asymmetric allylations

We have designed and synthesized a small library of modular monodentate diamidophosphite ligands with stereogenic phosphorus atoms. The library was prepared efficiently from the commercially available and inexpensive (S)-N-Boc-amino acids. These novel ligands were screened in the Pd-catalyzed asymmetric allylations of (E)-1,3-diphenylallyl acetate with dimethyl malonate as the C-nucleophile with up to 93% ee being obtained. The results showed that the different substituents in the 1,3,2-diazaphospholidine cycle had remarkable effects on the enantioselectivity.     

Forming a beam of ions extracted from glow-discharge plasma

In plasma-emitting structures based on glow-discharge, the potential difference between the ion-emitting plasma and the screening electrode of an ion-optic system depends on particular features of the electrode system of glow discharge and can vary in a range 0–1 kV. Results are presented of an experimental study and computer simulation of the formation of ion beams with ion energy 0–1 keV and current density 1–10 mA/cm² in ion sources based on such structures.     

Hard mode of stimulated scattering in the system of quasi-two-dimensional exciton polaritons

Dynamics of stimulated scattering of quasi-two-dimensional exciton polaritons in a semiconductor microcavity is considered theoretically. A system possessing a bistable response to coherent excitation is studied. Being a system of weakly interacting Bose particles under strongly nonequilibrium conditions, it exhibits a complex dynamics of the development of condensate modes. It is shown that multimode instability can arise in a threshold way in the system under a smooth increase in pump intensity. In this case, rapid populating of a multitude of unstable modes leads to stochastization of scattering, and evolution to a quasi-steady macrostate is performed as self-organization in an open nonequilibrium system. Arising fluctuations lead to the occurrence of a spatial nonuniformity of the distribution of scattered states.     

Study of zirconia microporous structure

The microporous structure of zirconium dioxide obtained by precipitation at different pH and different times of gel aging is studied by the physical adsorption of nitrogen, oxygen, and molecular hydrogen. It is shown that the ratio between the supermicropore surface areas measured by the adsorption of O₂ and N₂ as a function of the supermicropore volume previously revealed for SnO₂ is also retained for zirconia (the surface area of supermicropores measured by O₂ adsorption is larger than that measured by N₂ adsorption). Possible reasons for this phenomenon are discussed. The conclusions on the factors responsible for the formation of the zirconia microporous structure are drawn     

Long-term crack resistance of aging viscoelastic composite in static loading

The safe load and crack aging period are determined for an aging orthotropic plate on the basis of the theory of subcritical crack growth, which was proposed by A. A. Kaminskii. As an example, the safe load and crack incubation period are plotted for a ferroconcrete plate. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Prikladnaya Mekhanika, Vol. 35, No. 2, pp. 85–89, February, 1999.