Er^3＋掺杂钨酸铅晶体的发光和光谱特征

本试验测试了Er^3＋掺杂钨酸铅晶体（PbWO4：Er^3＋）的吸收光谱，依据J-O理论，首次计算报道了光谱项特征：J-O强度参数、量子荧光效率、荧光分支比等，Ω2=3．75×10^-20cm^2，Ω4=0．67×10^-20cm^2，Ω6=0．41×10^-20cm^2。计算证实，PWO：Er^3＋中几乎有80％的激发能量非辐射跃迁转移致^4I13／2能级，^4I13／2的计算寿命是5200μs，J-O计算显示，在PWO中产生^4I13/2→^4I15/2和发射1．53μm．有高的几率。讨论了不同浓度E

Yb∶Y3Al5O12晶体晶格振动光谱的研究

采用提拉法生长Y3Al5O12(YAG)晶体和Yb3+掺杂原子数分数分别为5%, 10%, 15%, 20%, 25%, 50%和100%的Yb∶Y3Al5O12(Yb∶YAG)晶体。系统表征和分析了Yb3+掺杂浓度对拉曼光谱的影响。随着Yb3+掺杂浓度的增加,晶体的振动模式没有明显的变化,晶体结构没有改变;在370 cm-1和785 cm-1附近,振动吸收峰的半峰全宽逐渐增大。分析得出,Yb3+掺杂浓度对晶体的晶格、对称性、荧光寿命均有影响,从而可能影响到晶体的光谱和激光性能。

Yb:YAP与Yb:YAG晶体光谱性能比较

应用中频感应提拉法生长出掺杂浓度为10 at.-%的Yb:YAG与Yb:YAP晶体，对比了室温下两种晶体的吸收和发射光谱特性。结果表明，Yb:YAG晶体比Yb:YAP晶体有更好的激光性能和低的阈值；同时对比发现，Yb:YAP晶体的吸收截面是Yb:YAG晶体的2.16倍，它容易实现LD泵；由于Yb:YAP晶体的各向异性，它有轴向效应明显，它可以产生偏振激光。

First-principles study of the electronic structures and absorption spectra for the PbMoO4 crystal with lead vacancy

The electronic structures and absorption spectra for the perfect PbMoO4 crystal and the crystal containing lead vacancy V-Pb(2-) with lattice structure optimized are calculated using density functional theory code CASTEP. The calculated absorption spectra of the PbMoO4 crystal containing V-Pb(2-) exhibit three absorption bands peaking at 2.0 eV (620 nm), 3.0 eV (413 run) and 3.3 eV (375 nm), which are in good agreement with experimental values. The theory predicts that the 390 nm, 430 nm and 580 run absorption bands are related to the existence of V-Pb(2-) in the PbMoO4 crystal.

Growth and annealing properties of Mg0.4Al2.4O4 crystal

Mg0.4Al2.4O4 single crystals with good optical quality were successfully grown by the Czochralski method. The transmission spectrum indicated that the absorption edge of the crystal was at 220nm, while no apparent absorption peaks were found. The X-ray diffraction and DSC curve analysis showed that Mg0.4Al2.4O4 crystal was stable at room temperature. While after annealing in the air and hydrogen atmosphere at about 1200 degrees C,Mg0.4Al2.4O4 decomposed into Al2O3 and (MgO)(0.4)(Al2O3)(x) (0.4 < x < 1.2). The reaction mainly occurred on the crystal surface, barely inside. (C) 2008 Elsevier B.V. All rights reserved.

Luminescence emission originating from nitrogen doping of beta-Ga2O3 nanowires

Nitrogen-doped beta-Ga2O3 nanowires (GaO NWs) were prepared by annealing the as-grown nanowires in an ammonia atmosphere. The optical properties of the nitrogen-doped GaO NWs were studied by measurements of the photoluminescence and phosphorescence decay at the temperature range between 10 and 300 K. The experimental results revealed that nitrogen doping in GaO NWs induced a novel intensive red-light emission around 1.67 eV, with a characteristic decay time around 136 mus at 77 K, much shorter than that of the blue emission (a decay time of 457 mus). The time decay and temperature-dependent luminescence spectra were calculated theoretically based on a donor-acceptor pair model, which is in excellent agreement with the experimental data. This result suggests that the observed novel red-light emission originates from the recombination of an electron trapped on a donor due to oxygen vacancies and a hole trapped on an acceptor due to nitrogen doping.

Influence of exotic Mn on magnetic properties of YCo5.0-xMnxGa7.0 (0.05 <= x <= 3.0)

The YCo5.0-xMnxGa7.0 compounds crystallize with the ScFe6Ga6-type structure. The lattice of YCo5.0-xMnxGa7.0 expands with the increase of the Mn content for 0.05 <= x <= 2.5, but the lattice of YCo2.0Mn3.0Ga7.0 shrinks compared with YCo2.5Mn2.5Ga7.0. The shrinkage of the lattice is attributed to the magnetostriction of YCo2.0Mn3.0Ga7.0. The substitution of Mn for Co forms magnetic clusters in the antiferromagnetic matrix. The magnetic frustration results in the spin-glass-like behavior for 0.8 <= x <= 1.5 and the difference between zero-field-cooling (ZFC) and field-cooling (FC) magnetizations for x = 2.0, 2.5, and 3.0. A stable long-range magnetic ordering appears among the Mn-centered magnetic clusters with the ordering temperature 110 K for x = 2.0. The hump in the thermomagnetization of YCo3.0Mn2.0Ga7.0 can be attributed to the competitive effects between the thermal fluctuation and the enhanced magnetic interaction. Both the hump and the bifurcation between the ZFC and the FC magnetizations of YCo3.0Mn2.0Ga7.0 occur at lower temperatures as the applied field increases. On the two-step magnetization curve of YCo3.0Mn2.0Ga7.0, the inflection point at 4000 Oe is due to the coercive field, and the magnetic moments in the clusters are tilted to the applied field above 4000 Oe. The magnetic ordering temperature is further increased to 210 K for x = 2.5 and to 282 K for x = 3.0. The spontaneous magnetization of YCo2.0Mn3.0Ga7.0 is 0.575 mu B/f.u. at 5 K with a canted magnetic structure.

Effect of substrate temperature on the growth and photoluminescence properties of vertically aligned ZnO nanostructures

Vertically well-aligned ZnO nanoridge, nanorod, nanorod-nanowall junction, and nanotip arrays have been successfully synthesized on Si (100) substrates using a pulsed laser deposition prepared ZnO film as seed layer by thermal evaporation method. Experimental results illustrated that the growth of different morphologies of ZnO nanostructures was strongly dependent upon substrate temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that the ZnO nanostructures were single crystals with a wurtzite structure. Compared with those of the other nanostructures, the photoluminescence (PL) spectrum of nanorod-nanowall junctions showed the largest intensity ratio of ultraviolet (UV) to yellow-green emission and the smallest full-width at half-maximum (FWHM) of the UV peak, reflecting the high optical quality and nearly defect free of crystal structure. The vertical alignment of the nanowire array on the substrate is attributed to the epitaxial growth of the nanostructures from the ZnO buffer layer. The growth mechanism was also discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.

Room-temperature ferromagnetic semiconductor MnxGa1-xSb

Ferromagnetic semiconductor MnxGa1-xSb single crystals were fabricated by Mn-ions implantation, deposition, and the post annealing. Magnetic hysteresis-loops in the MnxGa1-xSb single crystals were obtained at room temperature (300 K). The structure of the ferromagnetic semiconductor MnxGa1-xSb single crystal was analyzed by Xray diffraction. The distribution of carrier concentrations in MnxGa1-xSb was investigated by electrochemical capacitance-voltage profiler. The content of Mn in MnxGa1-xSb varied gradually from x = 0.09 near the surface to x = 0 in the wafer inner analyzed by X-ray diffraction. Electrochemical capacitance-voltage profiler reveals that the concentration of p-type carriers in MnxGa1-xSb is as high as 1 X 10(21) cm(-3), indicating that most of the Mn atoms in MnxGa1-xSb take the site of Ga, and play a role of acceptors.

Polarity determination for GaN thin films by electron energy-loss spectroscopy

The intensity of the N K edge in electron energy-loss spectra from a GaN thin film shows a pronounced difference when the orientation of the film approaches the (0002) and (000-2) Bragg reflections, along the polar direction. This experimental result can be interpreted by the effect associated with interference between the Bloch waves of the incident electron in the GaN crystal. The theoretical calculations indicate that, at the Bragg condition of g=0002 along the Ga-N bond direction, the thickness-averaged electron current density on the N atom plane is much higher than that at g=000 (2) over bar, with a maximum as the specimen thickness is about 0.4xi(0002) (the two-beam extinction distance). The delocalization effect on the experimental spectra is also discussed. (C) 2002 American Institute of Physics.

Content analyses in GaMnAs by double-crystal X-ray diffraction

A model for analyzing point defects in compound crystals was improved. Based on this modified model, a method for measuring Mn content in GaMnAs was established. A technique for eliminating the zero-drift-error was also established in the experiments of X-ray diffraction. With these methods, the Mn content in GaMnAs single crystals fabricated by the ion-beam epitaxy system was analyzed.

Improved purity of long-wavelength InAsSb epilayers grown by melt epitaxy in fused silica boats

In this study, we first present the process of the melt epitaxial (ME) growth method, and the improvement of low-temperature electron mobility of the long-wavelength InAsSb epilayers grown by ME in a fused silica boat. The electrical properties were investigated by van der Pauw measurement at 300 and 77 K. It is seen that the electron mobility of the InAsSb samples grown by graphite boat decreased from 55,700 to 26,600 cm(2)/V s when the temperature was reduced from 300 to 77 K, while for the samples grown by fused silica boat, the electron mobility increased from 52,600 at 300 K to 54,400 cm(2)/V s at 77 K. The electron mobility of 54,400cm(2)/Vs is the best result, so far, for the InAsSb materials with cutoff wavelength of 8-12 mum at 77 K. This may be attributed to the reduction of the carbon contamination by using a fused silica boat instead of a graphite boat. (C) 2002 Elsevier Science B.V. All rights reserved.

Polarity dependence of hexagonal GaN films on two opposite c faces of Al2O3 substrate

GaN films were grown in pairs on two opposite c faces of Al2O3 substrate by low-pressure metal-organic vapor phase epitaxy, and studied by scanning electron microscopy and converged beam electron diffraction. It is found that GaN film on the c-Al2O3 whose c face is forward to its crystal seed has [0001] polarity, and the other film on the C-Al2O3 whose c face is backward to its crystal seed has [000 (1) over bar] polarity. (C) 2001 American Institute of Physics.

Point defects in III-V compound semiconductors

Point defects in III-V compound semiconductors were analyzed systematically in this paper. The effects of substitutes, antisites, interstitials, and vacancies on lattice parameters in III-V compound semiconductors were calculated with a simple model. The formation energies of vacancies in compound semiconductors can be obtained by this calculation. A practical technique established on this model has been utilized for measuring the stoichiometry in GaAs. The relationship between stoichiometry and deep level centers in GaAs was also investigated.

New modulation structures observed in Bi2.13Sr1.87CuO6+delta superconductors

A new two-dimensional structure modulation along c- and b-axes has been discovered in superconducting single crystals of Bi2.13Sr1.87CuO6+delta (Bi2201) by x-ray scattering. Such modulation structure does not exist in non-superconducting Bi2201 single crystals, but instead lattice distortions are observed in the a-b-plane. This phenomenon may indicate that both strain relaxation and charge modulation in the a-b-plane are important to the occurrence of superconductivity in the copper oxides.