Investigation of the Photoluminescence of Individual Emission Bands of Mn2+ Ions in ZnS Plastically Strained Single Crystals

The photoluminescence spectra of ZnS : Mn plastically deformed single crystals are investigated. It is established that the plastic strain causes the relative concentrations of individual manganese emission centers to change together with conditions of excitation of the centers whose nearest environment has been rearranged upon plastic strain.     

Hydrogen atoms in impurity-helium solids

Electron spin resonance (ESR) is employed to study atomic impurities (H and D) stabilized in impurity-helium (Im-He) solids at 1.35-1.5 K. The kinetics of the low temperature tunneling exchange reactions (D+H2-->H+HD, D+HD-->H+D2) are investigated in Im-He samples containing several different mixtures of hydrogen and deuterium impurities. The ESR line structures help determine the local environment of atoms trapped in Im-He solids. High concentrations of atomic hydrogen stored in Im-He solids may ultimately find applications in energy storage, matrix-isolation spectroscopy, and studies of different quantum statistical effects.     

Luminescent Properties of the Surface of ZnS–Mn Nanocrystals Obtained by Self-Propagating High-Temperature Synthesis

Journal of Applied Spectroscopy - Luminescence of nanocrystalline ZnS–Mn powder obtained by self-propagating high-temperature synthesis is studied. The luminescence was excited by chemical...     

Noble-gas nanoclusters with fivefold symmetry stabilized in superfluid helium

Macroscopic samples (volume approximately cm(3), atomic density approximately 10(19) -10(20) cm(-3)) of noble-gas nanoclusters (size approximately 5-6 nm) were produced in superfluid helium by an impurity-helium gas injection technique. X-ray diffraction measurements show that the samples consist of weakly interacting nanoclusters with fivefold symmetry, such as icosahedra and decahedra. These results open new opportunities for fundamental research of nanoclusters of noble gases and other materials in well-controlled environments using experimental techniques requiring bulk samples.     

Gas-phase spectra of the radiative recombination of nitrogen atoms at helium temperatures

The lowering of temperature from ≈ 300 K to ≈ 10 K caused drastic changes in the spectral composition of the recombinational afterglow of N atoms: the glow due to the B³Π_gν″ | A ³Σ⁺_uν″ transition with ν′ = 12-9 (λ ≈ 580 nm and λ ≈ 540 nm) disappeared whereas levels with ν′ = 8-5 (λ ≈ 560 nm) appeared. This effect is exlained in terms of Campbell and Thrush's recombination luminescence model (emitting B ³H_g state populated by radiationless transition from the lower A ³Σ⁺_u state of the N₂ molecule).     

Effect of the electric fields of immobile dislocations on photoluminescence and EPR in deformed ZnS crystals

The influence of the electric fields of immobile growth dislocations on the luminescence properties of deformed zinc sulfide crystals is considered. Variations in the photoluminescence and EPR spectra with plastic deformation of ZnS crystals are shown to be caused by an increase in the radius of Read cylinders during the breakaway of growth dislocations from Cottrell atmospheres.     

Photoluminescence of manganese-doped LiNaGe4O9 crystals

The excitation spectra and photoluminescence spectra of manganese-doped LiNaGe₄O₉ crystals have been studied experimentally. It has been shown that the manganese ions provide strong red and weak yellow-green luminescences, whose intensities differently change upon the transition of the crystal from the paraelectric to ferroelectric phase. The possible localization and charge state of the manganese ions in LiNaGe₄O₉ crystals have been discussed.     

Chain length effect on the crystal thermal stability of oligoesters crystallized in thin layers

Specific heat of two fractions of oligomeric ethylene adipates (EA-2 with molecular weight <M _n>=1700 and EA-4 <M _n>=4000) containing up to 85 weight parts of untreated Aerosil-175, was measured in the temperature range 150–400 K. Detailed analysis of experimental data in terms of equations (1) and (2) led to the conclusion that significantly higher rate of decrease of both crystalline melting point as well as true (i. e., corrected for crystallinity) enthalpy of fusion with inverse value of distance between filler particles for EA-2 reflects higher affinity of end hydroxyl groups of oligomer chains in extended conformation towards polar Aerosil surface, as compared to that for middle-chain segments of EA-4 molecules which presumably are in a coiled conformation in the melt, and fold back on themselves on crystallization. On the other hand, sudden drop of experimental heats of fusion and crystallinities for both oligomers at filler contents above 50 weight parts is attributed to drastic jump of nucleation barrier for crystallization due to severe loss of conformational entropy of oligomer chains which either form ties between filler particles, with end groups anchored on the latter (as in the case of EA-2), or are squeezed in coiled conformation, with middle-chain segments on the periphery of coils interacting with neighboring filler particles (EA-4).     

Metastable impurity-helium solid phase. Experimental and theoretical evidence

A novel solid metastable phase of “sticking-together” helium van der Waals coats surrounding polarizable heavy impurities - Ne, Ar, Kr, Xe, N and N₂ - has been obtained and investigated using the experimental technique based on gas beam injection into superfluid helium. The element composition for this phase was measured and for all inert gases the solid samples were found to consist of more than 90% helium atoms and to keep stability up to T ≈ 8 K. The cluster approach to the theoretical analysis of the model NeHe₁₂ structures developed makes it possible to suggest the main physical reason for its formation to be the breakdown of quantum-mechanical helium atoms behavior, namely, strong suppression of amplitudes of radial zeroth vibrations for helium atoms belonging to the van der Waals shell in the field of dispersion forces of the central impurity particle. The phase diagram for the impurity-helium substance has been simulated and the direction of future investigations have also been outlined.     

Exotic behavior of hydrogen atoms in solid H2 at temperatures below 1 K

We present the first magnetic resonance study of atomic hydrogen embedded in solid H2 films for temperatures 150-900 mK. We found that at T approximately 150 mK average concentrations of H atoms of order 10(18 cm(-3) are very stable against recombination during two weeks of observations. The distribution of the population of the two lowest hyperfine states is found to be non-Boltzmann, with a very large occupation of the ground state. We consider the possibility of formation in solid H2 of regions with high local concentrations of H atoms, where collective quantum phenomena might occur.