Enhanced high-temperature thermoelectric performance of Yb(14-x)Ca(x)MnSb11

The high temperature p-type thermoelectric material Yb(14)MnSb(11) has been of increasing research interest since its high temperature thermoelectric properties were first measured in 2006. Subsequent substitutions of Zn, Al, and La into the structure have shown that this material can be further optimized by altering the carrier concentration or by reduction of spin-disorder scattering. Here the properties of the Yb(14-x)Ca(x)MnSb(11) solid solution series where isovalent Ca(2+) is substituted for Yb(2+) will be presented. Crystals of the Yb(14-x)Ca(x)MnSb(11) solid solution series were made by Sn-flux (x = 2, 4, 6, 8) with the following ratio of elements: (14-x)Yb: xCa: 6 Mn: 11Sb: 86Sn, and their structures determined by single crystal X-ray diffraction. The density of the material significantly decreases by over 2 g/cm(3) as more Ca is added (from x = 1 to 8), because of the lighter mass of Ca. The resulting lower density is beneficial from a device manufacturing perspective where there is often a trade-off with the specific power per kilogram. The compounds crystallize in the Ca(14)AlSb(11) structure type. The Ca substitution contributes to systematic lengthening the Mn-Sb bond while shortening the Sb-Sb bond in the 3 atom linear unit with increasing amounts of Ca. Temperature dependent thermoelectric properties, Seebeck, electrical resistivity, and thermal conductivity were measured from room temperature to 1273 K. Substitution of Yb with Ca improves the Seebeck coefficient while decreasing the thermal conductivity, along with decreasing the carrier concentration in this p-type material resulting in an enhanced thermoelectric figure of merit, zT, compared to Yb(14)MnSb(11).     

Homoleptic imidazolate frameworks [Sr(1-x)Eu(x)(Im)2]--hybrid materials with efficient and tuneable luminescence

Homoleptic frameworks of the formula [Sr(1-x)Eu(x)(Im)(2)] (1) (x = 0.01-1.0; Im(-) = imidazolate anion, C(3)H(3)N(2)(-)) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495-508 nm via variation of the europium content. The series of frameworks [Sr(1-x)Eu(x)(Im)(2)] presents dense MOFs with the highest quantum yields reported for MOFs so far.     

Nanostructuring, compositional fluctuations, and atomic ordering in the thermoelectric materials AgPb(m)SbTe(2+m). The myth of solid solutions

The nature of the thermoelectric materials Ag(1-x)Pb(m)SbTe(m+2) or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, infinity) are consistent with pure phases crystallizing in the NaCl-structure-type (Fmm) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range ordering of Ag, Pb, and Sb atoms. The long range ordering can be confirmed by single crystal X-ray diffraction studies. Indeed, data collections of five different single crystals were successfully refined in space groups of lower symmetry than Fmm including P4/mmm and Rm. The results reported here provide experimental evidence for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions.     

A Model for Simultaneous Homogeneous and Heterogeneous Nucleation in the Case of Slow Reaction Rate

(Gd(x)Y(1-x))(2)O(3):Eu [x=0, 0.25, 0.5, 0.75, 1.0] phosphor particles with 6 at.% Eu dopant of total concentration were prepared using spray pyrolysis. The effects of composition on the morphology, crystallinity, and photoluminescence characteristics of composite particles were investigated. The morphological control of (Gd(x)Y(1-x))(2)O(3):Eu particles in spray pyrolysis was also attempted by using colloidal and aqueous solutions. The particles prepared from colloidal solutions containing small amounts of Gd or Y hydroxy carbonate sol as seed material had spherical and filled morphology after the post-treatment at high temperature. On the other hand, the (Gd(x)Y(1-x))(2)O(3):Eu particles prepared from aqueous solutions were hollow and porous after post-treatment in all compositions. Particles prepared from colloidal solutions had photoluminescence emission intensities higher than those of particles prepared from aqueous solutions. Copyright 2000 Academic Press.     

CaMn(1-x)Nb(x)O3 (x < or = 0.08) perovskite-type phases as promising new high-temperature n-type thermoelectric materials

Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.     

One-pot noninjection synthesis of Cu-doped Zn(x)Cd(1-x)S nanocrystals with emission color tunable over entire visible spectrum

Unlike Mn doped quantum dots (d-dots), the emission color of Cu dopant in Cu d-dots is dependent on the nature, size, and composition of host nanocrystals (NCs). The tunable Cu dopant emission has been achieved via tuning the particle size of host NCs in previous reports. In this paper, for the first time we doped Cu impurity in Zn(x)Cd(1-x)S alloyed NCs and tuned the dopant emission in the whole visible spectrum via variation of the stoichiometric ratio of Zn/Cd precursors in the host Zn(x)Cd(1-x)S alloyed NCs. A facile noninjection and low cost approach for the synthesis of Cu:Zn(x)Cd(1-x)S d-dots was reported. The optical properties and structure of the obtained Cu:Zn(x)Cd(1-x)S d-dots have been characterized by UV-vis spectroscopy, photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). The influences of various experimental variables, including Zn/Cd ratio, reaction temperature, and Cu dopant concentration, on the optical properties of Cu dopant emission have been systematically investigated. The as-prepared Cu:Zn(x)Cd(1-x)S d-dots did show PL emission but with quite low quantum yield (QY) (typically below 6%). With the deposition of ZnS shell around the Cu:Zn(x)Cd(1-x)S core NCs, the PL QY increased substantially with a maximum value of 65%. More importantly, the high PL QY can be preserved when the initial oil-soluble d-dots were transferred into aqueous media via ligand replacement by mercaptoundeconic acid. In addition, these d-dots have thermal stability up to 250 °C.     

Spinodal decomposition and nucleation and growth as a means to bulk nanostructured thermoelectrics: enhanced performance in Pb(1-x)Sn(x)Te-PbS

The solid-state transformation phenomena of spinodal decomposition and nucleation and growth are presented as tools to create nanostructured thermoelectric materials with very low thermal conductivity and greatly enhanced figure of merit. The systems (PbTe)(1-x)(PbS)(x) and (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) are not solid solutions but phase separate into PbTe-rich and PbS-rich regions to produce coherent nanoscale heterogeneities that severely depress the lattice thermal conductivity. For x > approximately 0.03 the materials are ordered on three submicrometer length scales. Transmission electron microscopy reveals both spinodal decomposition and nucleation and growth phenomena the relative magnitude of which varies with x. We show that the (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) system, despite its nanostructured nature, maintains a high electron mobility (>100 cm(2)/V x s at 700 K). At x approximately 0.08 the material achieves a very low room-temperature lattice thermal conductivity of approximately 0.4 W/m x K. This value is only 28% of the PbTe lattice thermal conductivity at room temperature. The inhibition of heat flow in this system is caused by nanostructure-induced acoustic impedance mismatch between the PbTe-rich and PbS-rich regions. As a result the thermoelectric properties of (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) at x = 0.04, 0.08, and 0.16 were found to be superior to those of PbTe by almost a factor of 2. The relative importance of the two observed modes of nanostructuring, spinodal decomposition and nucleation and growth, in suppressing the thermal conductivity was assessed in this work, and we can conclude that the latter mode seems more effective in doing so. The promise of such a system for high efficiency is highlighted by a ZT approximately 1.50 at 642 K for x approximately 0.08.     

K3[Tb(x)Eu(1-x)Ge3O8(OH)2] (x = 1, 0.88, 0.67, 0): 2D-layered lanthanide germanates with tunable photoluminescent properties

A family of novel 2D-layered lanthanide germanates K(3)[Tb(x)Eu(1-x)Ge(3)O(8)(OH)(2)] (x = 1, 0.88, 0.67, 0; denoted as TbGeO-JU-87, Tb(0.88)Eu(0.12)GeO-JU-87, Tb(0.67)Eu(0.33)GeO-JU-87, and EuGeO-JU-87) were synthesized under mild hydrothermal conditions in a concentrated gel system. They are isostructural, as confirmed by the powder X-ray diffraction analysis. The single-crystal X-ray diffraction analysis of EuGeO-JU-87 reveals that it is a 2D-layered [EuGe(3)O(8)(OH)(2)](n)(3n-) anionic framework, which is built up from GeO(4)H/GeO(4) tetrahedra and EuO(6) octahedra by sharing vertex O atoms. Charge neutrality is achieved by K(+) ions located in the free void space. Interestingly, photoluminescence studies show that Tb(0.88)Eu(0.12)GeO-JU-87 and Tb(0.67)Eu(0.33)GeO-JU-87 exhibit a high Tb(3+)-to-Eu(3+) energy-transfer efficiency and the Tb(x)Eu(1-x)GeO-JU-87 system displays tunable photoluminescent properties.     

Large scale synthesis of stable tricolor Zn(1-x)Cd(x)Se core/multishell nanocrystals via a facile phosphine-free colloidal method

Here we report a new "green" method to synthesize Zn(1-x)Cd(x)Se (x = 0-1) and stable red-green-blue tricolor Zn(1-x)Cd(x)Se core/shell nanocrystals using only low cost, phosphine-free and environmentally friendly reagents. The first excitonic absorption peak and photoluminescence (PL) position of the Zn(1-x)Cd(x)Se nanocrystals (the value of x is in the range 0.005-0.2) can be fixed to any position in the range 456-540 nm. There is no red or blue shift in the entire reaction process. Three similar sizes of alloyed Zn(1-x)Cd(x)Se nanocrystals with blue, green, and yellow emissions were successfully selected as cores to synthesize high quality blue, green, and red core/shell nanocrystal emitters. For the synthesis of core/shell nanocrystals with a high quantum yield (QY) and stability, the selection of shell materials has been proven to be very important. Therefore, alternative protocols have been used to optimize thick shell growth. ZnSe/ZnSe(x)S(1-x) and CdS/Zn(1-x)Cd(x)S have been found as an excellent middle multishell to overcoat between the alloyed Zn(1-x)Cd(x)Se core and ZnS outshell. The QYs of the as-synthesized core/shell alloyed Zn(1-x)Cd(x)Se nanocrystals can reach 40-75%. The Cd content is reduced to less than 0.1% for Zn(1 -x)Cd(x)Se core/shell nanocrystals with emissions in the range 456-540 nm. More than 15 g of high quality Zn(1-x)Cd(x)Se core/shell nanocrystals were prepared successfully in a large scale, one-pot reaction. Importantly, the emissions of such thick multishell nanocrystals are not susceptible to ligand loss and stability in various physiological conditions.     

Origin of Thermal Degradation of Sr(2-x)Si(5)N(8):Eu(x) Phosphors in Air for Light-Emitting Diodes

The orange-red emitting phosphors based on M(2)Si(5)N(8):Eu (M = Sr, Ba) are widely utilized in white light-emitting diodes (WLEDs) because of their improvement of the color rendering index (CRI), which is brilliant for warm white light emission. Nitride-based phosphors are adopted in high-performance applications because of their excellent thermal and chemical stabilities. A series of nitridosilicate phosphor compounds, M(2-x)Si(5)N(8):Eu(x) (M = Sr, Ba), were prepared by solid-state reaction. The thermal degradation in air was only observed in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10, but it did not appear in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.02 and Ba analogue with x = 0.10. This is an unprecedented investigation to study this phenomenon in the stable nitrides. The crystal structural variation upon heating treatment of these compounds was carried out using the in situ XRD measurements. The valence of Eu ions in these compounds was determined by electron spectroscopy for chemical analysis (ESCA) and X-ray absorption near-edge structure (XANES) spectroscopy. The morphology of these materials was examined by transmission electron microscopy (TEM). Combining all results, it is concluded that the origin of the thermal degradation in Sr(2-x)Si(5)N(8):Eu(x) with x = 0.10 is due to the formation of an amorphous layer on the surface of the nitride phosphor grain during oxidative heating treatment, which results in the oxidation of Eu ions from divalent to trivalent. This study provides a new perspective for the impact of the degradation problem as a consequence of heating processes in luminescent materials.     

Influence of a nano phase segregation on the thermoelectric properties of the p-type doped stannite compound Cu(2+x)Zn(1-x)GeSe4

Engineering nanostructure in bulk thermoelectric materials has recently been established as an effective approach to scatter phonons, reducing the phonon mean free path, without simultaneously decreasing the electron mean free path for an improvement of the performance of thermoelectric materials. Herein the synthesis, phase stability, and thermoelectric properties of the solid solutions Cu(2+x)Zn(1-x)GeSe(4) (x = 0-0.1) are reported. The substitution of Zn(2+) with Cu(+) introduces holes as charge carriers in the system and results in an enhancement of the thermoelectric efficiency. Nano-sized impurities formed via phase segregation at higher dopant contents have been identified and are located at the grain boundaries of the material. The impurities lead to enhanced phonon scattering, a significant reduction in lattice thermal conductivity, and therefore an increase in the thermoelectric figure of merit in these materials. This study also reveals the existence of an insulator-to-metal transition at 450 K.     

Structural characterization and oxidative dehydrogenation activity of V2O5/Ce(x)Zr(1-x)O2/SiO2 catalysts

The thermal stability of a nanosized Ce(x)Zr(1-x)O2 solid solution on a silica surface and the dispersion behavior of V2O5 over Ce(x)Zr(1-x)O2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/Ce(x)Zr(1-x)O2/SiO2 catalyst. Ce(x)Zr(1-x)O2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined Ce(x)Zr(1-x)O2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/Ce(x)Zr(1-x)O2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of Ce(x)Zr(1-x)O2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/Ce(x)Zr(1-x)O2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of approximately 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce(x)Zr(1-x)O2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce(x)Zr(1-x)O2 to prevent the deactivation of supported vanadium oxide leading to stable activity in the time-on-stream experiments and high selectivity to styrene are other important observations.     

Solvothermal syntheses of [Ln(en)3(H2O)x(mu(3-x)-SbS4)] (Ln = La, x = 0; Ln = Nd, x = 1) and [Ln(en)4]SbS4.0.5en (Ln = Eu, Dy, Yb): a systematic study on the formation and crystal structures of new lanthanide thioantimonates(V)

New lanthanide thioantimonate(V) compounds, [Ln(en)3(H2O)x(mu(3-x)-SbS4)] (en = ethylenediamine, Ln = La, x = 0, Ia; Ln = Nd, x = 1, Ib) and [Ln(en)4]SbS4.0.5en (Ln = Eu, IIa; Dy, IIb; Yb, IIc), were synthesized under mild solvothermal conditions by reacting Ln2O3, Sb, and S in en at 140 degrees C. These compounds were classified as two types according to the molecular structures. The crystal structure of type I (Ia and Ib) consists of one-dimensional neutral [Ln(en)3(H2O)x(mu(3-x)-SbS(4))]infinity (x = 0 or 1) chains, in which SbS4(3-) anions act as tridentate or bidentate bridging ligands to interlink [Ln(en)3]3+ ions, while the crystal structure of type II (IIa, IIb, and IIc) contains isolated [Ln(en)4]3+ cations, tetrahedral SbS4(3-) anions, and free en molecules. A systematic investigation of the crystal structures of the five lanthanide compounds, as well as two reported compounds, clarifies the relationship between the molecular structure and the entity of the lanthanide(III) series, such as the stability of the lanthanide(III)-en complexes, the coordination number, and the ionic radii of the metals.     

Nanostructured Bi(2-x)Cu(x)S3 bulk materials with enhanced thermoelectric performance

Nanostructured Bi(2-x)Cu(x)S(3) (x = 0, 0.002, 0.005, 0.007, 0.01, 0.03) thermoelectric polycrystals were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) methods. The effect of Cu content on the microstructure and thermoelectric property of Bi(2-x)Cu(x)S(3) bulk samples was investigated. It was found that the subtle tailoring of Cu content could reduce both the electrical resistivity and the thermal conductivity at the same time, and consequently enhancing the thermoelectric property. A low electrical resistivity of 1.34 × 10(-4)Ω m(-1) and a low thermal conductivity of 0.52 W m(-1) K(-1) were obtained for the Bi(1.995)Cu(0.005)S(3) sample at 573 K. The low thermal conductivity is supposed to be due to the nanoscopic Cu-rich regions embedded in the host matrix. A peak ZT value of 0.34 at 573 K was achieved for the Bi(1.995)Cu(0.005)S(3) composition, which is the highest value in the Bi(2)S(3) system reported so far.     

Magneto-optical properties of Cd(1-x)Mn(x)S nanoparticles: influences of magnetic doping, Mn2+ ions localization, and quantum confinement

Cd(1-x)Mn(x)S nanoparticles (NPs) were successfully grown in a glass matrix and investigated by optical absorption (OA), magnetic circularly polarized photoluminescence (MCPL) measurements, and magnetic force microscopy (MFM). The room temperature OA spectra have revealed the formation of two groups of Cd(1-x)Mn(x)S NPs with different sizes: bulk-like nanocrystals (NCs) and quantum dots (QDs). The MCPL spectra were recorded at 2.0 K with several magnetic fields up to 15 T, allowing a detailed comparison between the degrees of circular polarization of the two groups of NPs. The different behaviours of magneto-optical properties of bulk-like NCs and QDs were explained by taking into account a considerable alteration of exchange interaction between the carrier spins and the substitutional doping magnetic ions incorporated into the NPs. As a main result, we have demonstrated that self-purification is the dominant mechanism that controls the doping in semiconductor QDs grown by the melting-nucleation synthesis approach due to the relatively high temperature that was used in thermal annealing of samples.     

Synthesis, crystal and electronic structures of the new quaternary phases A5Cd2Sb5F (A = Sr, Ba, Eu), and Ba5Cd2Sb5O(x) (0.5<x<0.7)

A new family of quaternary fluoro-antimonides A(5)Cd(2)Sb(5)F (A = Sr, Ba, Eu) and oxyantimonides Ba(5)Cd(2)Sb(5)O(x) (0.5相似文献   

Tunable electrical and magnetic properties of half-metallic Zn(x)Fe(3-x)O4 from first principles

The electrical and magnetic properties of Zn-doped Fe(3)O(4) at different doping concentrations of Zn have been investigated using a density functional method with generalized-gradient approximation corrected for on-site Coulombic interactions. The electronic structure calculation predicts that Zn(x)Fe(3-x)O(4) (0 ≤x≤ 0.875) is half-metallic with a full spin polarization. The hopping carrier concentration of Zn(x)Fe(3-x)O(4) decreases with increasing x, which indicates a distinct increase in the resistivity. The saturation magnetization of Zn(x)Fe(3-x)O(4) increases evidently with increasing x from x = 0 to x = 0.75 (i.e. from 4.0 to 8.3 μ(B)/f.u.) and then decreases rapidly to zero at x = 1. The robust half-metallicity, large tunability of electrical and magnetic properties of a Zn doped Fe(3)O(4) system make it a promising functional material for spintronic applications.     

Structure and white luminescence of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials

The optical properties of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials have been determined after the structural reinvestigation of the hypothetical Ba 13Al 22Si 10O 66 material on the basis of the Gebert's model. The white fluorescence and phosphorescence of the (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66:Eu series result from the existence of two broad emission bands associated with (8)H-4f(6)5d(1)-->(8)S-4f(7) transitions peaking at 534 and 438 nm, the intensities of which may be tuned at room temperature via the control of the europium concentration and the substitution of Sr for Ba. This suggests the possibility to adjust the emission of the material to white LED requisites.     

Enhanced luminescence of rare-earth complexes Tb(1-x)Eu(x)(m-NBA)3Phen in ZnS

Rare-earth ternary complexes Tb(1-x)Eu(x)(m-NBA)(3)Phen (X=1, 0.25, 0.5, 0.75, 1.0) were synthesized and characterized by IR, DTA-TG, UV, fluorescent spectra and elemental analysis. It was found that luminescence of Eu(3+) complex was enhanced by doped with Tb(3+). It is proved by TG curve that the complexes are stable, ranging from ambient temperature to 360 degrees C in air. The organic-inorganic combined structural device was fabricated, and the electroluminescence intensity of the combined structural device was improved compared with the device of the purely organic components.     

Photoluminescence and Raman scattering from catalytically grown Zn(x)Cd(1-x)Se alloy nanowires

Zn(x)Cd(1-x)Se alloy nanowires, with composition x = 0, 0.2, 0.5, 0.7, and 1, have been successfully synthesized by a chemical vapor deposition (CVD) method assisted with laser ablation. The as-synthesized alloy nanowires, 60-150 nm in diameter and several tens of micrometers in length, complied with a typical vapor-liquid-solid (VLS) growth mechanism. The Zn(x)Cd(1-x)Se nanowires are single crystalline revealed from high-resolution transmission electron microscopic (HRTEM) images, selected area electron diffraction (SAED) patterns, and X-ray diffraction (XRD) measurement. Compositions of the alloy nanowires can be adjusted by varying the precursor ratios of the laser ablated target and the CVD deposition temperature. Crystalline structures of the Zn(x)Cd(1-x)Se nanowires are hexagonal wurtzite at x = 0, 0.2, and 0.5 with the [0 1 -1 0] growth direction and zinc blende at x = 0.7 and 1 with the [1 -1 1] growth direction. Energy gaps of the Zn(x)Cd(1-x)Se nanowires, determined from micro-photoluminescence (PL) measurements, change nonlinearly as a quadratic function of x with a bowing parameter of approximately 0.45 eV. Strong PL from the Zn(x)Cd(1-x)Se nanowires can be tuned from red (712 nm) to blue (463 nm) with x varying from 0 to 1 and has demonstrated that the alloy nanowires have potential applications in optical and sensory nanotechnology. Micro-Raman shifts of the longitudinal optical (LO) phonon mode observed in the Zn(x)Cd(1-x)Se nanowires show a one-mode behavior pattern following the prediction of a modified random element isodisplacement (MREI) model.