Sensitized UV luminescence from single crystals of zinc oxide

The reflection, absorption, excitation, photoluminescence, and cathodoluminescence spectra have been studied for indium-doped single crystals of ZnO. The temperature quenching of the UV-radiation bands has also been studied. These studies have made it possible to establish that the UV-radiation bands are excited during quantum absorption corresponding to “band-band” transitions and also by exciton absorption. The studies have also made it possible to calculate the activation energy of the temperature quenching. In the photoluminescence spectrum of ZnO crystals there is a wide radiation band in the 3950–4050-Å region which could be described by transitions in donor-acceptor pairs. It is shown that the band of the equidistant series at 3834 Å is complex in character.     

Optical resonators with inhomogeneous mirrors

It is shown that the possibility of changing a laser light beam intensity distribution exists when the output mirror transmittance depends on the transverse plane coordinates. Methods of manufacture of inhomogeneously transmitting laser mirrors with constant phase of the reflected beam over the whole surface are described. Two examples of application of such systems are considered: one for obtaining a laser beam with constant intensity distribution in the transverse plane, the other for single-segment energy extraction from high-order transverse modes. The total laser output power is shown to be almost the same as for use of a homogeneous output mirror.     

Thermally Stimulated Electron–Hole and Ionic Processes in Zinc Oxide Crystals

The principal results of the investigation of thermally stimulated electron–hole and ionic processes in hydrothermal and gas-phase ZnO single crystals preexcited at low temperatures, based on simultaneous study of photo-EPR and thermoluminescence (TL), are presented. The nature of the traps determining the TL peaks at 17, 24, 40, 53, 90–110, 140–150, and 160–200 K is discussed. In particular, it has been established that the lithium paramagnetic centers (Li_Zn ⁺–O^I) play the role of hole traps in ZnO giving green and red TL in the temperature range 160–200 K and, in the case of association with small-sized donors, also TL in the temperature range 90–110 K. The other traps are electronic in character, and in the presence of acceptor lithium in the crystals, they form yellow-orange TL. Optical quenching of TL has been evaluated, and it has been found that there is a difference E 0.75 eV between the thermal and optical energies of ionization of lithium acceptors. Irreversible ionic processes associated with the healing of cationic vacancies at T 360–420 K have been revealed.     

Neutron nano-spin-echo spectrometer based on magnetic nanostructures

A neutron spin-echo spectrometer based on spin precessors in the form of magnetic layered nanostructures is described. A model of a spin-echo spectrometer is developed on beam no. 9 in the IBR-2 reactor. In this model, spin precession occurs during motion of neutrons in a magnetic field and their double reflection from Al(30 nm)/Fe(15 nm)/Al(120 nm)/Cu(150 nm) magnetic layered structures. The obtained spectrometer parameters make it possible to investigate excitations in films with a wave vector oriented along the neutron beam direction in the range from 10^?3 to 10^?1 Å^?1 and perpendicularly to the beam in the range from 10^?4 to 10^?5 Å^?1.     

Line emission of sodium and hydroxyl radicals in single-bubble sonoluminescence

Spectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chloride solutions with a defined concentration of argon were performed as a function of the driving acoustic pressure. The broad-band continuum ranging from 200 to 700 nm is characterized by fits using Planck's law of blackbody radiation. The obtained blackbody temperatures are in the range of 10(4) K and are revealed to be independent of the presence of a salt and the acoustic pressure, whereas the SL intensity increases by a factor of more than 10 within the studied acoustic pressure range. The different trends followed by SL intensity and blackbody temperatures question the blackbody model. In solutions with 70 mbar of argon, line emissions of OH(?) radicals and Na* are observed. The shape of the OH(?) radical emission spectrum is very similar to that in MBSL spectra, indicating the strong similarity of intrabubble conditions. An increase of the acoustic pressure causes the continuum to overlap the lines until they become indistinguishable. The emission line of Na* in NaCl is observed only at high NaCl concentrations. When sodium dodecylsulfate is used a pronounced Na* line is already observed in a 1 mM solution thanks to enrichment of sodium ions at the interface. The results presented in this work reveal the strong similarity of SBSL and MBSL under certain experimental conditions.     

Balance of neutrons during their transport through magnetic noncollinear and noncoplanar layered systems

The violation of the detailed balance principle (DBP) for polarized neutrons during their mirror reflection and transport through a two-layered noncollinear magnetic structure in a magnetic field (noncoplanar system), and without it (noncollinear system), is revealed. Moreover, the existence of left-right non-polarized neutron transmission asymmetry for a noncoplanar layered system is uncovered.     

Determination of the local structure of a highly dispersed Pd-Nanosystem located on a titanium dioxide carrier

This work is devoted to a structural study of a highly dispersed Pd nanosystem, which is stabilized in the TiO₂ matrix, by XAFS spectroscopy. Nanocomposite was prepared from bimetallic PdCo(μ-OOCMe)₄(NCMe) precursor followed by processing in several ways: calcination in air and in argon and microwave irradiation. The local structure of Pd catalysts formed by different methods was studied. Possible structural models were considered in detail.     

Potential applications of sonochemistry in spent nuclear fuel reprocessing: A short review

The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems. The dissolution of refractory solids, ultrasonically driven liquid–liquid extraction and the sonochemical degradation of the volatile products of organic solvent radiolysis issued from PUREX process are considered. Also the guidelines for required further work to ensure successful application of the studied processes at industrial scale are discussed.     

On splitting of dislocations at a reverse motion in germanium single crystals

The dislocation dissociation after the reverse motion along a slip plane in Ge single crystals have been investigated. It has been established that the dissociation width as well as the constriction density were independent on the motion direction. The results obtained have been used to clarify the role of the dislocation splitting in the formation of the phenomenon of the dislocation mobility asymmetry.