Luminescence kinetics of crystalline and vitreous silicon dioxide

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 5, pp. 800–805, November, 1991.     

Luminescence of different modifications of crystalline silicon dioxide: Stishovite and coesite

Luminescence of very small samples of single crystals of coesite and stishovite has been studied. The spectra were detected under ionizing radiation (X-ray and electron beam) and the decay kinetics of cathodoluminescence in the range of time from 10 ns to 3 ms was measured. The coesite luminescence possesses a broad band at 3 eV with exponential decay about 680 μs at 80 K. The nature of this luminescence was explained as a self-trapped exciton creation in tetrahedron framework. The stishovite luminescence possesses two bands—blue (2.8 eV) and UV (4.7 eV). The UV band intensity grows more than 20 times with irradiation dose from initial level. This shows that the corresponding luminescence centers could be induced by the radiation. The decay of the UV band possesses a fast and a slow component. The determination of the fast decay parameters is beyond the capabilities of our apparatus (less than 10 ns), whereas the slow decay of the UV is non-exponential and takes place in the range of hundreds of microsecond. The blue band decay kinetics can be well approximated by power law ∼t⁻², which may correspond to recombination of defects created by radiation. The stishovite single crystal luminescence is very similar to that of germanium dioxide single crystal of rutile structure. The nature of the stishovite luminescence is explained as recombination of defects created by irradiation in octahedron-structured lattice.     

Energy transport in silica to oxygen-deficient luminescence centers. Comparison with other luminescence centers in silica and α-quartz

The transport of energy absorbed by silica glass to oxygen-deficient luminescence centers in was studied in the range of intrinsic absorption from 8.2 up to 35 eV. The low efficiency of exciting those luminescence centers by transport of energy could not be ascribed merely to carrier scattering by the disordered structure. Other centers (Cu⁺, for example) could be excited in such process with sufficiently high efficiency, albeit lower than that in crystals. The low efficiency of interaction of oxygen deficient centers with quasi-particles is attributed to isolation of these centers in clusters and the non-radiative annihilation of the quasi-particles on the boundaries of these clusters with the main network.     

A combinatorially convenient version of synthesis of 5-substituted oxazole-4-carboxylic acid ethyl esters

Reaction of ethyl isocyanoacetic acid with sodium hydride in anhydrous benzene, followed by treatment with carboxylic acid chlorides or N-(acyloxy)pyrrolidine-2,5-diones, gives 5-substituted oxazole-4-carboxylic acid esters. The procedure is applicable to derivatives of various carboxylic acids, including saturated aliphatic, α,β-unsaturated, alicyclic, aromatic, heterocyclic, and N-Boc-protected amino acids.     

Synthesis of 4-Aryl-5-nitro-1,2,3-triazoles

Russian Journal of Organic Chemistry -     

Dynamic surface tension and surface rheology of biological liquids

The paper presents results of dynamic and equilibrium surface tension measurements (using a maximum bubble pressure instrument) of serum and urine samples that were obtained from 80 healthy human of various sexes and ages. These data were compared with surface tension measurements of biological liquids obtained from patients suffering from malignant neoplasm of corpus uteri (n=5) and cervix uteri (n=31). In addition, surface dilatational rheology was determined on 32 samples using a drop shape method. The dilatational rheology data were compared with the dynamic surface tension data. Although some trends were found, no significant correlations exist between surface tension and rheology data and any of the disease states or stages. It is difficult to explain these findings in the framework of known mechanisms. However, our studies demonstrate that dynamic interface tensiometry of human biological liquids provide new insight into the biophysical behavior of these liquids, most likely reflecting compositional changes of them during ageing, the course of cancer and as a consequence of therapeutical interventions.     

Arylation of geminally activated nitroethenes

3-Aryl-2-nitroprop-2-enenitriles and 1,3-diphenyl-2-nitroprop-2-en-1-one reacted with N,N-dimethylaniline to give the corresponding arylation products, 3-aryl-3-(4-dimethylaminophenyl)-2-nitropropanenitriles and 3-(4-dimethylaminophenyl)-1,3-diphenyl-2-nitropropan-1-one, whose structure was confirmed by IR and ¹H and ¹³C-{¹H} spectroscopy with the use of ¹H-¹³C HMQC and HMBC heteronuclear correlation techniques.     

The puzzles of natural ferrimagnetics

Paleomagnetic studies have revealed that natural ferrimagnetics, which are constituents of igneous rocks, can be magnetized antiparallel to the magnetizing field. This phenomenon is called self-reversal of magnetization. The question of the actual existence of inversions of the geomagnetic field is still under investigation. This paper considers the physics of the anomalous behavior of natural ferrimagnetic thermomagnetization (TM). The existence of thermomagnetization arising in natural ferrites against the direction of a magnetizing field is experimentally confirmed. It is shown that even after the demagnetization of a ferrimagnetic by alternating magnetic field a significant increase in residual magnetization can occur when it is heated in the absence of a magnetic field.     

Investigation of composition and energy processes on the surface of electrodes of a lead-acid accumulator

Oxidation-reduction reactions (Pb ↔ Pb _x O _y ) without participation of sulfur and sulfates were found to take place on the surface of electrodes of a lead-acid accumulator during its operation and charging. The investigation was performed using the technique of spectroscopy of backscattered low-energy ions, Auger-spectroscopy and secondary-ion mass spectroscopy.