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《Radiation measurements》2007,42(4-5):644-647
The tetragonal : persistent luminescence materials were prepared by a solid state reaction. The UV excited and persistent luminescence was observed in the green region centred at 535 nm. Both luminescence phenomena are due to the same ion occupying the single site in the host lattice. The codoping usually reduced the persistent luminescence of :, which differs from the : and : materials. Only the ion enhanced slightly the persistent luminescence. With the aid of synchrotron radiation, the band gap energy of : was found to be about 7 eV that is very similar to those of the : materials. Thermoluminescence results suggested that the ions might act as electron traps, but only the TL peaks created by and can be found in the temperature range accessible. Lattice defects (e.g. oxygen vacancies) are also important, since the same main thermoluminescence peak was observed at about with and without codoping. 相似文献
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《Radiation measurements》2008,43(1):1-4
Time-resolved luminescence spectra from quartz can be separated into components with distinct principal and secondary lifetimes depending on certain combinations of annealing and measurement temperature. The influence of annealing on properties of the lifetimes related to irradiation dose and temperature of measurement has been investigated in sedimentary quartz annealed at various temperatures up to . Time-resolved luminescence for use in the analysis was pulse stimulated from samples at 470 nm between 20 and . Luminescence lifetimes decrease with measurement temperature due to increasing thermal effect on the associated luminescence with an activation energy of thermal quenching equal to for the secondary lifetime but only qualitatively so for the principal lifetime component. Concerning the influence of annealing temperature, luminescence lifetimes measured at are constant at about for annealing temperatures up to but decrease to about when the annealing temperature is increased to . In addition, it was found that lifetime components in samples annealed at are independent of radiation dose in the range 85–1340 Gy investigated. The dependence of lifetimes on both the annealing temperature and magnitude of radiation dose is described as being due to the increasing importance of a particular recombination centre in the luminescence emission process as a result of dynamic hole transfer between non-radiative and radiative luminescence centres. 相似文献
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The real compact supergroup is analysed from different perspectives and its representation theory is studied. We prove it is the only (up to isomorphism) supergroup, which is a real form of with reduced Lie group , and a link with SUSY structures on is established. We describe a large family of complex semisimple representations of and we show that any -representation whose weights are all nonzero is a direct sum of members of our family. We also compute the matrix elements of the members of this family and we give a proof of the Peter–Weyl theorem for . 相似文献
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《Radiation measurements》2007,42(4-5):843-846
Absorption and emission spectra, luminescence decay kinetics and thermostimulated luminescence of X-ray irradiated YAG:Yb single crystalline films were studied. Two emission bands peaked at 420 and 488 nm have been detected in the investigated films. The strong thermal quenching of luminescence band at 488 nm was observed above 160 K. The influence of growth conditions and annealing in air on the lifetime of ion excited state in the IR spectral region have been revealed. The recombination mechanisms of the transition at ion excitation, as well as the mechanism of lifetime shortening for the excited luminescence have been discussed. 相似文献
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Zhao-Yi Zeng Cui-E Hu Ling-Cang Cai Xiang-Rong Chen Fu-Qian Jing 《Solid State Communications》2009,149(47-48):2164-2168
We have performed detailed first-principles calculations to investigate the structural and lattice dynamical properties of NiTi alloy. The calculated static structures consist well with the experimental data and other theoretical results. With quasi harmonic approximation, the phase boundary between B19′ and BCO phases can be described as a five order polynomial . The change of vibrational entropy is /atom at the transition temperature 100 K under zero pressure. 相似文献
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Negative thermal expansion materials can experience significant stresses when they are used in composites. Under ambient conditions Zr2(WO4)(PO4)2 displays anisotropic negative thermal expansion (NTE) (, , , at 0 GPa). The effect of hydrostatic pressure on its thermal expansion characteristics was investigated by neutron diffraction between 300 and 60 K at pressures up to 0.3 GPa. No phase transitions were observed in the pressure and temperature range examined. The material was found to have a bulk modulus, B0, of 61.3(8) GPa at ambient temperature, and unlike some other NTE materials, pressure had no detectable effect on thermal expansion (, , , at 0.3 GPa). 相似文献
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We give an explicit construction of the -cocycles of the group of contactomorphisms on the supercircle for , with coefficients in the space of differential operators acting on -tensor densities. We show that they satisfy properties similar to those of the super-Schwarzian derivative. 相似文献
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Connection, torsion and curvature are introduced for general (local) Leibniz algebroids. Generalized Bismut connection on is an example leading to a scalar curvature of the form for a closed -form . 相似文献
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In this paper, first we introduce a new notion of pseudo anti-commuting for real hypersurfaces in complex two-plane Grassmannians and prove a complete classification theorem, which gives a shrinking Ricci soliton with potential Reeb flow on Hopf real hypersurfaces and a tube over a totally real totally geodesic , in . 相似文献
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-monopoles are solutions to gauge theoretical equations on noncompact -manifolds of holonomy. We shall study this equation on the Bryant–Salamon manifolds. We construct examples of -monopoles on two of these manifolds, namely the total space of the bundle of anti-self-dual two forms over the and . These are the first nontrivial examples of -monopoles.Associated with each monopole there is a parameter , known as the mass of the monopole. We prove that under a symmetry assumption, for each given there is a unique monopole with mass . We also find explicit irreducible -instantons on and on .The third Bryant–Salamon -metric lives on the spinor bundle over the -sphere. In this case we produce a vanishing theorem for monopoles. 相似文献
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In terms of quantum Fisher information, we discuss the dynamics of quantity of the Ising model. The inequality detects the class of entangled states which are useful for sub-shot-noise sensitivity. All the exact dynamics of the expectations of collective spin operators are derived. The minimum in the plane perpendicular to the mean spin direction is analytically given. We find that does not depend on the system size when . Except for the periodic points, the evolution states are always entangled and useful for the sub-shot-noise phase estimation. 相似文献
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《Physica A》2006,365(1):217-221