共查询到20条相似文献,搜索用时 31 毫秒
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Rongjin Huang Laifeng Li Zhixiong Wu Xinxin Chu Xiangdong Xu Lihe Qian 《Solid State Communications》2010,150(35-36):1617-1620
Antiperovskite manganese nitrides (, 0.1, 0.15) were prepared and their negative thermal expansion, magnetic and specific heat properties were investigated. A frozen state with a freezing temperature was found at ~207 K in . This indicates that exhibits a spin glass state at low temperatures. We discussed the cause of spin glass behavior and correlated this spin glass behavior with broadening of the negative thermal expansion operation-temperature window of the manganese nitrides . 相似文献
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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》2007,42(4-5):719-722
Luminescence and luminescence excitation under VUV radiation of (, K, Cs; , In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated crystals. The band structure and partial densities of electronic states of perfect , and crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made. 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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《Journal of Geometry and Physics》2007,57(1):89-100
In this paper we study a generalized Darboux Halphen system given by where , , are real variables, are real constants and We prove that, for any , this system does not admit any non-constant global first integral that can be described by a formal power series. Furthermore, restricting the values of to a full Lebesgue measure set, we prove that this system does not admit any non-constant rational or Darbouxian global first integral. This is a first step toward proving that this system is chaotic. 相似文献
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《Radiation measurements》2007,42(4-5):874-877
Ytterbium doped borate crystals are promising laser media, e.g. in (LSB) matrices large distance between ytterbium ions results in reduced concentration quenching of the ytterbium f–f luminescence [Petermann, K., Fagundes-Peters, D., Johansen, O., Mond, M., Peters, V., Romero, J.J., Kutovoi, S., Speiser, J., Giesen, A., 2005. Highly Yb-doped oxides for thin-disc lasers. J. Crystal Growth 275, 135-140]. ions in complex oxides in addition to the 4f 4f transitions often manifest fast charge transfer luminescence (CTL) in the UV-visible range. In some borates it was not observed at all, like in orthoborates of Sc, Y and La [Van Pieterson, L., Heeroma, M., de Heer, E., Meijerink, A., 2000. Charge transfer luminescence of . J. Lumin. 91, 177–193]; in haloborates , where X = Cl, Br, the UV/visible luminescence was attributed to ytterbium CTL though it looked substantially different from other matrices [Dotsenko, V.P., Berezovskaya, I.V., Pyrogenko, P.V., Efryushina, N.P., Rodniy, P.A., Eijk van, C.W.E., Sidorenko, A.V., 2002. Valence states and luminescence properties of ytterbium ions in strontium haloborates. J. Solid State Chem. 166, 271–276]; while in oxyborate “classical” CTL was observed [Jubera, V., Garcia, A., Chaminade, J.P., Guillen, F., Sablayrolles, Jean, Fouassier, C., 2007. and luminescent properties of the phase. J. Lumin. 124(1), 10–14]. In this work the luminescence properties of another borate, namely LSB doped by Yb are presented. 相似文献
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《Radiation measurements》2008,43(8):1325-1330
A new glow curve fitting function is proposed for mixed-order kinetics. The free parameters of this function are the glow curve maximum , the temperature maximum , activation energy and ratio , where and are initial concentrations of electrons in active and inactive traps, respectively. The new fitting method for determination of the thermoluminescence (TL) parameters is checked for some characteristics values of the parameters. The characteristics of this obtained function are simplicity, clearness and precision. To get this function only analytical terms obtained out of mixed-order kinetics equation were used. There are no empirical terms. 相似文献