分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-03-30
摘要: Cerium doped gadolinium gallium aluminum oxide (GAGG:Ce) nanopowders were prepared by a co-precipitation method with different cation concentrations of the mother salt solution, followed by calcination at different temperatures. The influence of cation co
分类: 材料科学 >> 材料科学(综合) 提交时间: 2017-03-30
摘要: Cerium doped gadolinium gallium aluminum oxide (GAGG:Ce) nanopowders were prepared by a co-precipitation method with different cation concentrations of the mother salt solution, followed by calcination at different temperatures. The influence of cation co
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-04-06
摘要: We report the synergistic optimization of the thermoelectric properties in p-type Bi0.48Sb1.52Te3 by the additional graphene. Highly dense Bi0.48Sb1.52Te3 + graphene (x wt%, x = 0, 0.05, 0.1 and 0.15) composites have been synthesized by zone-melting follo
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A micron size YAG:Ce/YAG:Cr core–shell structure was designed and accomplished via the urea homogeneous precipitation method using the YAG:Ce spherical core as the introduced second phase. A well dispersed gel like encapsulation structure can be achieved before the formation of YAG:Ce/YAG:Cr core–shell particles via a calcination process. As prepared YAG:Ce/YAG:Cr particles can emit a broad range of photons from 500 to 750 nm with excitation light of 433 nm. A schematic illustration showing the mechanism of excitation–emission of the core–shell particles is presented. The integral spectra are composed of three parts: emission photons of YAG:Cr, YAG:Ce, and emission light of YAG:Cr excited by the emission photons of the YAG:Ce core according to the proposed mechanism. The method accomplished in this work can significantly improve the exploration of full spectrum luminescent powder synthesis and spectra designation.
提交时间: 2017-05-02
摘要: Urea precipitation method has been developed as an important approach for the preparation of inorganic particles with defined morphology and composition. In present work, we provide survey of the technological developments and achievements mainly on the a
提交时间: 2017-05-02
摘要: In order to obtain a uniform transparent ceramic scintillator, well-dispersed fine starting powders with high-purity, small grain size, spherical morphology and high sinter-ability are necessary. In this study, Ce3+ doped gadolinium aluminum gallium garne
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-08
摘要: The thermoelectric properties of two-dimensional graphyne sheets are investigated by using first- principles calculations and the Boltzmann transport equation method. The electronic structure indicates a semiconducting phase for graphyne, compared with the metallic phase of graphene. Consequently, the obtained Seebeck coefficient and the power factor of graphyne are much higher than those of graphene. The calculated phonon mean free path for graphene is 866 nm, which is in good agreement with the experimental value of 775 nm. Meanwhile the phonon mean free path of graphyne is only 60 nm, leading to two order lower thermal conductivity than graphene. We show that the low thermal conductivity of graphyne is due to its mixed sp/sp2 bonding. Our calculations show that the optimized ZT values of graphyne sheets can reach 5.3 at intermediate temperature by appropriate doping.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: A novel layered GGAG/YAG composite scintillation ceramic can be prepared at 1650◦C using an easily accessible preparation procedure. The oxygen sintering-hot isostatic pressing method implemented in this work can significantly shorten the preparation period of scintillation ceramics. The ceramic exhibits regular grain microstructure. Interface of the composite ceramic is clean and straight. As prepared, the layered Ce:GGAG/Cr:YAG composite ceramic can emit a broad range of photons with wavelength from 500 to 750 nm under excitation. The integral spectra is composed of three parts: emitted photons of Cr:YAG and Ce:GGAG and emitted light of Cr:YAG excitated by the photons emitted by the Ce:GGAG ceramic layerprepared by the proposed method. The method accomplished in this work can significantly improve the exploration of full spectrum scintillation/luminescence ceramics preparation and spectra designation.
提交时间: 2017-05-02
摘要: principles calculations. The obtained phonon frequencies agree well with the measurements of Raman scattering. The thermodynamic properties are calculated within quasi-harmonic approximation, and the measured lattice thermal conductivity is well reproduce
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Gadolinium gallium aluminum garnet (GGAG) is a very promising host for the highly efficient luminescence of Ce3+ and shows potential in radiation detection applications. However, the thermodynamically metastable structure would be slanted against it from getting high transparency. To stabilize the crystal structure of GGAG, Yb3+ ions were codoped at the Gd3+ site. It is found that the decomposition of garnet was suppressed and the transparency of GGAG ceramic was evidently improved. Moreover, the photo- luminescence of GGAG:Ce3+,xYb3+ with different Yb3+ contents has been investigated. When the Ce3+ ions were excited under 475 nm, a typical near-infrared region emission of Yb3+ ions can be observed, where silicon solar cells have the strongest absorption. Basing on the lifetimes of Ce3+ ions in the GGAG:Ce3+,xYb3+ sample, the transfer efficiency from Ce3+ to Yb3+ and the theoretical internal quantum efficiency can be calculated and reach up to 86% and 186%, respectively. This would make GGAG:Ce3+,Yb3+ a potential attractive downconversion candidate for improving the energy conversion efficiency of crystalline silicon (c-Si) solar cells.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: We obtained a single phase BLS:Eu2+, Ce3+, Mn2+ phosphor by solid-state reactions. Eu2+, Ce3+, and Mn2+ gives rise to the blue, green, and red emission, respectively. The Mn2+ red emission can be effectively enhanced via energy transfers from both Eu2+ and Ce3+. Thus a tunable full color emission from 410 to 750 nm was realized in this single phosphor. The Eu2+ ! Mn2+ energy transfer mechanism was investigated by the fluorescence decay curves. This single phosphor exhibits an efficient excitation band covering from 390 to 410 nm, which matches well with the emission light of the efficient NUV chips. The optimized BLS:Eu2+, Ce3+, Mn2+ phosphor shows a high quantum efficient of $62% and a good color stability. When this single phosphor was combined with a 395 nm NUV-chip, an ideal white LED with a high color render index (CRI) of 85 and a correlated color temperature (CCT) of 6300 K was obtained. This demonstrates the promising application of the BLS:Eu2+, Ce3+, Mn2+ single phosphor for the NUV-based white LEDs.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Tin telluride (SnTe) has recently attracted much attention as a promising thermoelectric material. In this work, SnTe is alloyed with additional Pb, and the high density crystalline ingots of SnPbxTe (x 1⁄4 0, 0.02, 0.04, and 0.06) have been synthesized by a zone-melting method. Through this method, SnPbxTe samples show larger power factors than those prepared by other methods, and a maximum value of 30.5 mW cm 1 K 2 at 823 K has been reached in p-type SnPb0.02Te, which is the highest value reported so far. As a result, a promising figure of merit ZT of $0.81 has been obtained at 823 K.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: SnCdxTe materials were synthesized by the zone-melting method for this thermoelectric performance study. The X-ray diffraction results show that the lattice parameter decreases with increasing x, following Vegard's law of rock-salt structure SnTe and CdTe. Besides, the room temperature Seebeck coefficients of the SnCdxTe system are enhanced to >60 mV K 1, larger than those of Cd-doped SnTe synthesized by spark plasma sintering. A large power factor of $25 mW cm 1 K 1 is achieved in SnCd0.12Te at 820 K, which rivals those of high performance PbTe-based materials. As a result, the highest ZT of $1.03 at 820 K was achieved for SnCd0.12Te.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: We study type I clathrate Ba8Cu5.1Ge40.2Sn0.7 single crystals (space group Pm3"n, no. 223, a 1⁄4 10.7151(3)) grown using a Sn flux method. Microprobe analysis and single-crystal X-ray diffraction reveal a small amount of Sn embedded in the Cu/Ge framework, which increases disorder at the guest Ba sites. Ba8Cu5.1Ge40.2Sn0.7 is diamagnetic with a susceptibility of $2.8 10 7 emu g 1 and shows metal-like behavior (dr/dT > 0) with a low charge carrier concentration of 0.5 e per unit cell at 300 K. The single crystals show a relatively high carrier mobility (m (300 K) 1⁄4 11.9 cm2 V 1) and very low lattice thermal conductivity ($0.6 W m 1 K 1). The thermoelectric figure of merit ZT of Ba8Cu5.1Ge40.2Sn0.7 single crystals reaches a maximum value of 0.6 at 773 K, which can be further improved by adjusting the chemical composition.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Tin selenide (SnSe) compound has attracted much attention due to its unprecedented high ZT (B2.6) in single crystals. The polycrystalline SnSe materials were then prepared to improve the mechanical performance for large-scaled application. However, the ZT values of 0.3–0.8 were much lower due to their poor electrical properties. In the present study, the zone melting method is employed to prepare the polycrystalline SnSe samples, which show highly textured structures and strong anisotropic thermoelectric performance. A maximum power factor (S2s) of 9.8 mW cm 1 K 2 was obtained in the polycrystalline samples, which is comparable with that of SnSe single crystals, resulting in a peak ZT of 0.92 at 873 K. The zone-melted ingot was then pulverized into powders and the bulk material was prepared by the spark plasma sintering (SPS) technique. As a result, the ZT value was enhanced to be over 1.0, owing to the slight reduction of lattice thermal conductivity and maintenance of electrical performance. The present investigation indicates that the TE performance of the SnSe compound can be significantly improved by the texture modulation.