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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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In this paper we investigate Leibniz algebras whose quotient Lie algebra is a naturally graded filiform Lie algebra . We introduce a Fock module for the algebra and provide classification of Leibniz algebras whose corresponding Lie algebra is the algebra with condition that the ideal is a Fock -module, where is the ideal generated by squares of elements from .We also consider Leibniz algebras with corresponding Lie algebra and such that the action gives rise to a minimal faithful representation of . The classification up to isomorphism of such Leibniz algebras is given for the case of . 相似文献
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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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We investigate the photoluminescence (PL) properties of silver/porous-silicon (Ag/PSi) nanocomposites prepared by metal-assisted etching in solution, on the basis of steady-state and time-resolved PL spectroscopy measurements. The PL intensity and peak position are strongly dependent on the concentration. Time-resolved PL measurements reveal that the nonradiative rate decreases with an increase in the concentration for the Ag/PSi nanocomposites. It is found from x-ray photoelectron spectroscopy measurements that the decrease in the nonradiative rate is caused by the formation of layers on the PSi surfaces. Further, the number of light-emitting Si nanocrystals in the nanocomposites, which is estimated from the PL decay rate and PL intensity, increases with the concentration. From the wavelength dependence of the PL decay rate, it is found that the nonradiative rate is considerably dispersive, i.e., the shorter the wavelength, the higher the nonradiative rate. 相似文献
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《Journal of Physics and Chemistry of Solids》2007,68(5-6):725-728
Metal//a-Si-/c-Si structures containing amorphous silicon nanoparticles (a-Si NPs) embedded in ultra thin matrix are fabricated by thermal evaporation of and sputtering of layers followed by thermal annealing at . A memory effect, due to charging of a-Si NPs in , is observed. The processes of NP charging and discharging are accomplished by applying pulses with alternative polarities. The observed shift of the flat band voltage of the high-frequency C–V curve caused by a voltage pulse of having duration of 1 s is more than 3 V. In addition, the structures show good retention characteristics which make them promising for application in non-volatile memory devices. 相似文献
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The pentagram map is now known to be a discrete integrable system. We show that the integrals for the pentagram map are constant along Poncelet families. That is, if and are two polygons in the same Poncelet family, and is a monodromy invariant for the pentagram map, then . Our proof combines complex analysis with an analysis of the geometry of a degenerating sequence of Poncelet polygons. 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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《Physica A》2005,350(1):38-44
Finite size effects on the calorimetric cooperatity of the folding-unfolding transition in two-state proteins are considered using the Go lattice models with and without side chains. We show that for models without side chains a dimensionless measure of calorimetric cooperativity defined as the ratio of the van’t Hoff to calorimetric enthalpy does not depend on the number of amino acids N. The average value is lower than the experimental value . For models with side chains approaches unity as , where . Above the critical chain length these models can mimic the truly all-or-non folding–unfolding transition. 相似文献