Thermal quenching of luminescence of BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals activated with Er<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

Thermal quenching of interconfigurational 5d-4f luminescence of Er³⁺ and Tm³⁺ ions in BaY₂F₈ crystals is studied in the temperature range of 330–790 K. The quenching temperatures are ~575 and ~550 K for Er³⁺ and Tm³⁺, respectively. It is shown that quenching of 5d-4f luminescence of Tm³⁺ ions is caused by thermally stimulated ionization of 5d electrons to the conduction band.     

Enhancement of optical luminescence of solids using a capillary lens

The Advanced Photon Source (APS) at Argonne National Laboratory is a 1-km-circumference, 7-GeV, third generation synchrotron light source. It is the largest light source in the Western Hemisphere and attracts about 3,500 users every year from around the globe. The APS is currently preparing for a major upgrade, a goal of which is to focus on high brightness at photon energies of around 20 keV and higher. The APS is particularly well suited for this high photon energy range due to its higher-energy, 7-GeV electron beam, but it also needs new insertion devices with short periods and high fields, i.e., superconducting devices.     

Structure of mechanically activated high-energy Al + polytetrafluoroethylene nanocomposites

The structure of high-energy Al/polytetrafluoroethylene nanocomposites prepared by mechanochemical synthesis is studied by X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, and chemical analysis. It is revealed that the composite consists of aluminum particles with sizes of 100–150 nm separated by the polymer layers. The formation of nanocomposite is accompanied by the accumulation of dislocations with the density ρ = (4 ± 1.5) × 10¹⁰ cm⁻². Upon the shock-wave initiation of activated samples, Al + (-C₂ F₄-) → AlF₃ + C reaction propagates in detonation-similar regime at supersonic speed. The velocity of detonation is the highest at the stoichiometric component ratio.     

Optimal rigidity of a thin-walled orthotropic cylinder in combined tension and torsion

The problem of optimizing the reinforcement of an orthotropic cylinder in combined torsion and tension is considered in relation to the condition of minimum displacement. A numerical example is given. It is shown that the stiffness depends on the ratio of the normal and shear stresses, the elastic moduli, and the parameters.Moscow Aviation Technological Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1121–1123, November–December, 1973.     

Method for estimating the acceleration ability of aluminized high explosives

A semiempirical method for calculating the acceleration ability of aluminized high explosives was developed using experimental data. The method is based on the assumption that the coefficient of transformation of chemical energy into the kinetic energy of the flyer depends on the number of moles of gaseous detonation products. The model takes into account the effective extent of oxidation of aluminum at various stages of motion of the flyer. Calculations were performed for compositions containing a number of new explosives. The calculation results show that nanostructured aluminized composite can be superior to mechanical mixture in acceleration ability if the main explosive has a highly negative oxygen balance or contains and enhanced amount of hydrogen.     

Emission and excitation spectra of Ce3+ and Pr3+ ions in hexafluoroelpasolite lattices

The emission and excitation spectra of Ce(3+) and Pr(3+) doped into the cubic host Cs(2)NaYF(6) have been recorded at room temperature and ～10 K using synchrotron radiation. The two 5d(1) T(2g) states of Ce(3+) have been located from the excitation spectra, whereas the E(g) state is placed above the host band gap. Decay measurements of the 5d(1) → 4f(1) Ce(3+) emission, and spectra collected using selective excitation, indicate the occupation of more than one type of site by Ce(3+) in this host lattice. By contrast, the location of features in the 4f(1)5d(1) → 4f(2) emission of Pr(3+) is independent of the excitation wavelength. Assignments are presented for some of the 4f(1)5d(1) levels and for the Pr(3+)-F(-) charge transfer band. The 5d emission lifetimes for Ce(3+) and Pr(3+) in the Cs(2)NaYF(6) host are 42 and 29 ± 1 ns, respectively, and are not temperature-dependent.     

Photoluminescence of Lu3Al5O12:Bi and Y3Al5O12:Bi single crystalline films

Single crystalline films of Lu₃Al₅O₁₂:Bi and Y₃Al₅O₁₂:Bi have been studied at 4.2–450 K by the time-resolved luminescence spectroscopy method. Their emission spectrum consists of two types of bands with strongly different characteristics. The ultraviolet band consists of two components, arising from the electronic transitions which correspond to the ³P₁ → ¹S₀ and ³P₀ → ¹S₀ transitions in a free Bi³⁺ ion. At T < 80 K, mainly the lower-energy component with the decay time ～10^?3 s is observed, arising from the metastable ³P₀ level. At T > 150 K, the higher-energy component prevails, arising from the thermally populated emitting ³P₁ level. The visible emission spectrum consists of two dominant strongly overlapped broad bands with large Stokes shifts. At 4.2 K, their decay times are ～10^?5 s and ～10^?4 s and decrease with increasing temperature. Both of the visible emission bands are assumed to be of an exciton origin. The lower-energy band is ascribed to an exciton, localized near a single Bi³⁺ ion. The higher-energy band, showing a stronger intensity dependence on the Bi³⁺ content, is assumed to arise from an exciton, localized near a dimer Bi³⁺ center. The structure of the corresponding excited states is considered, and the processes, taking place in these states, are discussed.     

Acceleration Ability of Aluminum-Containing Explosive Compositions

Results of a study of explosives with varying oxygen balance by a method based on the acceleration of a steel plate from the charge end face (M-40) have confirmed the possibility of increasing the acceleration ability of these substances owing to the addition of powdered aluminum. The experimental and calculated data suggest that, in the case of mixtures prepared by the conventional method of mechanical mixing, compositions with aluminum nanoparticles and compositions containing aluminum with a particle size on the order of a few microns have similar acceleration ability values. Nanocomposites—systems with a uniform distribution of aluminum nanoparticles in the explosive matrix—can be superior to the mechanical mixtures in acceleration ability in the case of a highly negative oxygen balance of the explosive base. Calculations have shown that the acceleration ability of mixtures of low-sensitivity explosives with aluminum can be further increased owing to the formation of nanocomposites.