High-efficiency erbium ion luminescence in silicon nanocrystal systems

The photoluminescence spectra and kinetics of both erbium-doped and undoped multilayer structures of quasi-ordered silicon nanocrystals in a silicon dioxide matrix were studied. It was shown that the optical excitation energy of silicon nanocrystals 2–3 nm in size can be practically completely transferred to Er³⁺ ions in the oxide surrounding the nanocrystals, with its subsequent radiation at 1.5 μm. Possible reasons for the high excitation efficiency of the Er³⁺ ions are discussed, and the conclusion is drawn that the F?rster mechanism is dominant in the energy transfer processes occurring in these structures. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 1, 2004, pp. 105–109. Original Russian Text Copyright ? 2004 by Kashkarov, Kamenev, Lisachenko, Shalygina, Timoshenko, Schmidt, Heitmann, Zacharias.     

Special points for calculating integrals over the primitive cell of a periodic system

A method is proposed for constructing appropriate sets of special points in the Brillouin zone in which the extended unit cell method is used with a subsequent shift from the center of the reduced Brillouin zone. The proposed method offers several advantages over the commonly used Monkhorst-Pack method. The difference in the construction of sets of special points for the direct and reciprocal lattices is discussed for crystals belonging to a nonsymmorphic space group. The cases of a planar square lattice and an fcc lattice are considered to illustrate general results.     

Green luminescence in diffusion-doped layers of zinc selenide

Diffusion-doped layers with a green emission band dominating in the room-temperature luminescence spectrum are obtained by annealing single-crystal zinc selenide substrates in tellurium and zinc vapors.     

Interrelation between anharmonicity and lateral strain in quasi-isotropic polycrystalline solids

A new formula that relates the acoustic Grüneisen parameter to the Poisson ratio is suggested on the basis of the previously derived expression for this parameter.     

Specific Features of Determining the Electrophysical Parameters of Variband CMT Structures Grown by Molecular-Beam Epitaxy

The effects of wide- and narrow- variband layers on the charge-carrier concentration and mobility in the MBE-grown epitaxial CMT structures measured by the Hall-effect method are studied by numerical simulation. The dependence of the relative difference between the experimentally obtained effective values of electrophysical parameters and those of an epitaxial coating on the variband-layer characteristics is discussed. An analysis of this dependence shows that the manner in which the broad-band and narrow-band layers affect the resulting parameters is inequivalent. The calculations suggest that the effect of the wide-band layer on the experimental electrophysical parameters can be neglected. In the case of the narrow variband layer, however, the difference between the electophysical parameters strongly depends on the variband-layer parameters and the concentrations of ionized donor and acceptor centers.     

To the Quantum Effects in Nuclear Fission

An assumption that the most probable fragments of spontaneous low-energy fission inherit the quantum structure of initial nuclei is discussed. The energies Q of spontaneous decay into two fragments of nuclei with 2 < Z < 102 are estimated. The transition from negative to positive values of Q occurs near Z = 40.     

On the Neutron Method of Transmutation of Nuclear Wastes

Russian Physics Journal -     

Anomalies in the Absorption and Reflection of a High-Power Ultrashort Laser Pulse by a Plasma with a Solid-State Density

The patterns of absorption and reflection of an ultrashort laser pulse by a plasma with a solid-state density, which are realized in the mode of the normal skin effect, are studied. It is shown that a decrease in low-power pulse duration shorter than the period corresponding to the fundamental frequency of radiation leads to an increase in the absorption coefficient. If the pulse power is so high as to provide electron heating during a time shorter than the reciprocal fundamental frequency, nonlinear suppression of absorption takes place and the spectrum of the reflected radiation contains odd harmonics of the fundamental frequency.