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排序方式: 共有71条查询结果,搜索用时 8 毫秒
31.
K.V. Ivanovskikh A. Meijerink A. Speghini C. Ronda M. Bettinelli 《Journal of luminescence》2010,130(5):893-16384
The silicates Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12, both undoped and doped with Pr3+ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca3Sc2Si3O12:Pr3+ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca3Y2Si3O12:Pr3+ and Ca3Lu2Si3O12:Pr3+ show features attributed to emission from two distinct sites accommodating the Pr3+ dopant. The decay kinetics of the Pr3+ 5d-4f emission in Ca3Sc2Si3O12:Pr3+ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence. 相似文献
32.
Fedor Gmry Laura Gherardi Giovanni Crotti Daniela Bettinelli Luciano Martini Luigi Bigoni Sergio Zannella 《Physica C: Superconductivity and its Applications》1998,310(1-4):168-172
AC losses were measured by 4-probe transport method and by external magnetization method in three samples of Bi-2223/Ag tape: a multifilamentary tape with separated filaments, another multifilamentary tape with ‘bridges' between filaments, and a two-shell tape. The transport losses agreed with those calculated using Ic from DC experiment. Magnetization experiments gave indications about the various paths of induced currents. For the tape with well separated filaments the main part of screening current closes inside individual filaments. Additional screening of the whole filamentary zone involves the normal metal matrix, leading to frequency dependent losses. In the case of tape with ‘bridged' filaments, supercurrents interconnect the filaments into bundles whose screening (and loss) is frequency-independent. Matching the experimental data indicates that a typical bundle was composed of 8 filaments. Magnetic losses of the two-shell tape were explained by a model for magnetization of superconducting wire with elliptical cross-section. 相似文献
33.
B.R. Jovanić M. Bettinelli F. Piccinelli B. Radenković M. Despotović-Zrakić Z. Bogdanović 《辐射效应与固体损伤》2013,168(7-8):574-583
This study considers the effects of hydrostatic pressure on the line position and fluorescence lifetime τ for 5D0 → 7F2 transitions in GdVO4: Eu3+ nanocrystals. The results indicate that the pressure induced the red shift toward longer wavelengths for all the considered lines with different rate. The fluorescence lifetime τ nonlinearly decreases with pressure in the considered pressure range. High pressure induced the fluorescence lifetime τ that can be explained with a simple theoretical model. The measured line position and τ are in a satisfactory agreement with the theoretical calculations. 相似文献
34.
Andrea Bettinelli Alberto Ceselli Giovanni Righini 《Annals of Operations Research》2010,179(1):221-241
In this paper we consider a variation of the bin packing problem in which bins of different types have different costs and
capacities. Furthermore, each bin has to be filled at least to a certain level, which depends on its type. We present a set
partitioning formulation and an exact optimization algorithm which exploits column generation and specialized heuristics.
We compare our algorithm with the general purpose solver ILOG CPLEX, running on two compact ILP formulations and we report
on experimental results on instances we have generated from data-sets for the variable size bin packing problem. 相似文献
35.
Rados?aw Lisiecki Witold Ryba-Romanowski Marco Bettinelli 《Journal of luminescence》2009,129(5):521-525
LaPO4 single crystals lightly doped with Er3+, and codoped with Er3+ and Yb3+ have been grown by spontaneous nucleation in a lead phosphate flux. Absorption and luminescence spectra have been measured in the visible and near-IR regions and the excited state dynamics has been studied upon pulsed laser excitation. The obtained results have allowed the evaluation of the effective emission cross-sections around 1.5 μm, that have been found to be similar to important oxide laser crystals doped with Er3+. Efficient visible upconversion has been observed upon excitation at 980 nm in the codoped crystals. This behaviour is attributed to Yb3+-Er3+ energy transfer processes. 相似文献
36.
D. Hreniak W. Stręk P. Głuchowski M. Bettinelli A. Speghini 《Applied physics. B, Lasers and optics》2008,91(1):89-93
Nd3+:Y3Al5O12 (Nd:YAG) powders were prepared by the Pechini method in the temperature range of 800 to 1400 °C. The pure garnet phase of
the obtained materials was confirmed by XRD studies. The size of the grains was controlled by the annealing temperature of
the samples. Their morphologies were investigated by TEM and porosity measurements (BET). The effect of annealing temperature
on the morphology and luminescence properties of Nd:YAG nanocrystallites was studied, and the results were compared to the
properties of a Nd:YAG single crystal. A significant enhancement of the 4F3/2→4I9/2/4F3/2→4I11/2 intensity ratio with decreasing grain size was observed. It was found that the decay times of the Nd3+ luminescence depends on the specific surface and is significantly longer for well crystallized nanocrystalline grains than
for single crystals having the same concentration of Nd3+ ions. The role of crystallinity and specific surface on the radiative processes is analyzed.
PACS 78.55.-m; 78.20.Ci; 78.67.Bf; 78.68.+m 相似文献
37.
V. Venkatramu D. Falcomer A. Speghini M. Bettinelli C.K. Jayasankar 《Journal of luminescence》2008,128(5-6):811-813
The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu3(1?x)Er3xGa5O12 powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er3+-doped Lu3Ga5O12 nanocrystalline samples have been measured. The decay curve of the (2H11/2,4S3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er3+ ions in Lu3Ga5O12 nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er3+-doped Lu3Ga5O12 in the form of nanocrystalline powders. 相似文献
38.
M.H. Bartl E.C. FuchsK. Gatterer H.P. FritzerM. Bettinelli A. Speghini 《Journal of solid state chemistry》2002,167(2):386-392
Single crystals of yttrium aluminium borate, YAl3(BO3)4, (referred to as YAB) doped with 20 and 40 mol% of Nd3+ were grown using a flux growth method. Inconsistencies in regard to the reported ground state splitting of the doped material are pointed out. A consistent splitting and assignment of the 4I9/2 ground state levels of the Kramers-ion Nd3+ was obtained by a combination of both, temperature-dependent 4I9/2→2P9/2 polarized absorption spectroscopy and room temperature 4F9/2→4I9/2 luminescence spectroscopy. The group theoretical implications of the crystal field analysis are considered and discussed. 相似文献
39.
Kumar KU Prathyusha VA Babu P Jayasankar CK Joshi AS Speghini A Bettinelli M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(3-4):702-708
The compositional and concentration dependence of luminescence of the (4)F(3/2)-->(4)I(J) (J=13/2, 11/2 and 9/2) transitions in four Nd(3+)-doped tellurite based glasses has been studied. The free-ion energy levels obtained for 60TeO(2)+39ZnO(2)+1.0Nd(2)O(3) (TZN10) glass have been analysed using the free-ion Hamiltonian model and compared with similar results obtained for Nd(3+):glass systems. The absorption spectrum of TZN10 glass has been analysed using the Judd-Ofelt theory. Relatively longer decay rates have been obtained for Nd(3+)-doped phosphotellurite glasses. The emission characteristics of the (4)F(3/2)-->(4)I(11/2) transition, of the Nd(3+):TZN10 glass, are found to be comparable to those obtained for Nd(3+):phosphate laser glasses. The non-exponential shape of the emission decay curves for the (4)F(3/2)-->(4)I(11/2) transition is attributed to the presence of energy transfer processes between the Nd(3+) ions. 相似文献
40.
S. Mahlik M. Grinberg A.A. Kaminskii M. Bettinelli P. Boutinaud 《Radiation measurements》2010,45(3-6):288-291
Photoluminescence and time resolved photoluminescence spectra of Ca(NbO3)2 doped with Pr3+, excited under 37,000 cm?1 (270 nm), obtained at high hydrostatic pressure up to 20 kbar applied in a sapphire anvil cells, are presented. At ambient conditions, the emission spectrum obtained in the time interval 0–1 μs is dominated by spin allowed transitions from the 3P0 state. The luminescence related to transitions from 1D2, characterized by a decay time equal to 33 μs, is observed when one excites directly the Pr3+ ion with 30,770 cm?1 (325 nm) wavelength. The introduction of Pr3+ impurities in Ca(NbO3)2 does not quench the self-trapped exciton (STE) luminescence. This luminescence, peaking at 20,000 cm?1 (500 nm), having a decay time of 61 ± 1 μs, still occurs when the crystal is excited with a wavelength of 37,000 cm?1 (270 nm) or shorter. Under such excitation a fraction of the STE luminescence is reabsorbed by Pr3+ ions; in this case the emission lifetime of the 1D2 → 3H4 transition of Pr3+ is 64 ± 3 μs. This effect is stable also at high pressure. 相似文献