Tunable emission properties of core-shell ZnCuInS-ZnS quantum dots with enhanced fluorescence intensity

Cadmium-free I-III-VI quantum dots (QDs), represented by Cu-In-S (CIS), are widely investigated for their non-toxicity and tunable emission properties. In this work, Zn-Cu-In-S (ZCIS) alloyed QDs were synthesized via a solvothermal approach by heating up a mixture of the corresponding metal precursors and sulphur powder with dodecanethiol in oleylamine media, and the fluorescent intensity was greatly enhanced by coating ZnS (ZS) shell. By changing the ratio of Cu, the as prepared ZCIS-ZS QDs showed composition-tunable photoluminescent (PL) emission over the visible spectral window from about 500 nm to 620 nm, which is much wider than that of CIS QDs. Moreover, the influence of excitation wavelength, reaction temperature and time on the optical properties of the ZCIS-ZS QDs was also studied. This research provides a feasible and simple approach to prepare ZCIS-ZS QDs with large tunable spectral range on visible region, which could greatly contribute to the development of potential applications due to their non-toxicity and excellent optical properties.     

具有自组装纳米结构的AIE光敏剂用于增强光动力治疗（英文）

基于具有聚集诱导发光(AIE)性质的2,3-双(4’-(二苯基)-[1,1’-联苯]-4-基]富甲腈(BDBF)分子,制备了三种纳米结构并用于图像引导光动力学治疗(PDT).普兰尼克F127可包封BDBF形成常见的球形纳米粒子(F127@BDBF NPs),该纳米粒子可发射红色荧光,荧光量子效率(FQY)为9.8%.此外, BDBF也可在水中自组装成纳米棒(BDBF NRs).与F127@BDBF NPs相比, BDBF NRs呈现出较强的橙色荧光,具有较高的荧光量子产率(23.3%),以及基本相同的单线态氧(1O2)产生能力.利用F127对BDBF NRs进行进一步修饰可得到BDBF@F127 NRs,该纳米粒子仍然保持了棒状形貌和较好的1O2产生能力.同时,与溶解态的BDBF相比,三种纳米结构的单线态氧产生效率增强.这些纳米结构在水溶液和生理条件下具有良好的稳定性.细胞的光毒性实验表明,三种纳米结构均能有效抑制肿瘤细胞增殖.因此,通过简单的自组装方法制备高荧光量子效率和较强单线态氧产生能力的纳米结构可作为一种有效的途径来增强光动力.     

Waveguide-modulated surface plasmon-coupled emission of Nile blue in poly(vinyl alcohol) thin films

Surface plasmon-coupled emission (SPCE) phenomenon is the coupling of excited fluorophores near a silver film with surface plasmons, resulting in directional emission into the underlying glass substrates. We report a complex coupling of Nile Blue fluorophore with 50 nm silver mirror, resulting in emission at several angles in the glass substrate, with either s or p polarization. This complex pattern of directional and polarized emission appears to be due to optical waveguide effects occurring when the sample thickness becomes comparable to the emission wavelength. We expect waveguide-modulated SPCE to have applications to biophysics and sensing.     

Energy transfer and enhanced 1532 nm emission in Er and Ce co-doped Y3Al5O12 nano-particles

A series of Y₃Al₅O₁₂:Ce³⁺, Er³⁺ (YAG:Ce, Er) nano-particles were synthesized by polymer-assisted sol–gel method. X-ray diffraction measurements reveal that a pure crystalline phase of YAG is achieved at temperature as low as 800 °C. The energy transfer from Ce³⁺ to Er³⁺ is studied based on photoluminescence spectroscopy and fluorescence decay patterns. It results that the emission intensity of Er³⁺ at near infrared (NIR) 1532 nm under indirect excitation of Ce³⁺ (460 nm) is 10 times stronger than that of direct excitation of Er³⁺ (275 or 380 nm). The energy transfer efficiency is estimated as 95.5% for YAG:Ce_0.03Er_0.09 sample. The very efficient energy transfer path and mechanism are also discussed.     

Observation of Non-Radiative Recombination Enhanced Point Defect Reaction in Semiconductors

IntroductionWide-bandgapcompoundsemiconductorsforblue-greenlaserdiodesandlight-emittingdiodeshavebeenintensivelystudiedinrecentyears.Ithasbeenrecognizedthatpre-existingdefectsplayasignificantroleinthedevicedegradation.Reductionofthesedefectshasbeentheprimaryeffortinachievingalonglifetimeoflight-emittingdevices.Inthispaper,wepresentourmainexperimentalresultsonthenonradiativerecombinationenhancedpointdefectreactioninsemiconductorsbydirectlymonitoringtheprocessofradiativeelectron-holerecombinatio…     

Enhanced emission from CaSi2O2N2:Eu phosphors by doping with Y ions

Yttrium doped CaSi₂O₂N₂:Eu²⁺ phosphors were prepared by the solid state reaction method. Large increases in the emission have been achieved by adding Y³⁺ ions in the host. XRD data revealed that the lattice expanded as doping Y³⁺ ions. XPS results suggested that there were more Eu²⁺ ions incorporated into the lattice of Y³⁺ doped samples than that of undoped samples. The doping effect of Y³⁺ ions has been discussed systematically. By using this novel Y³⁺ doped CaSi₂O₂N₂:Eu²⁺ phosphor, bright daylight emission with luminous efficiency (η_L) of 44 lm/W, color rendering index (CRI) of 82 and correlated color temperature (CCT) of 5300 K can be generated from white LED.     

Structural investigation and improvement of photoluminescence properties in Ba(ZrxTi1−x)O3 powders synthesized by the solid state reaction method

In this paper, Ba(Zr_xTi_1−x)O₃ powders with different (x) compositions were synthesized by the solid state reaction method and their structure and improvement of photoluminescence (PL) properties with the Ti substitution by Zr were discussed. The structural investigation of these powders was performed by means of X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman) spectroscopy. Their optical properties were monitored by ultraviolet–visible (UV–vis) absorption spectroscopy and PL measurements. XRD patterns indicated that the powders with x = 0 and 0.1 have a tetragonal structure while compositions with x ≥ 0.2 exhibit cubic structure. FT-Raman spectra revealed that the replacement of Ti by Zr significantly reduced the intensity of the Raman active modes. This behavior is related to the increase of undistorted [ZrO₆] clusters in the global matrix at short range and decrease in local concentration of distorted octahedral [TiO₆] clusters. UV–vis absorption spectra shown the presence of intermediary energy levels between the valence band (VB) and the conduction band (BC). These intermediary electronic levels are mainly related to 2p orbitals of O atoms, 4d orbitals of Zr atoms and 3d orbitals of Ti atoms between the VB and CB. A significant improvement in PL properties of Ba(Zr_xTi_1−x)O₃ powders was observed with an increase of undistorted [ZrO₆] clusters in the lattice. Finally, we propose possible wideband models based on intermediary energy deep and shallow levels to explain the PL behavior at room temperature.     

Surface exciton-plasmon polariton enhanced light emission via integration of single semiconductor nanowires with metal nanostructures

The light emission enhancement behavior from single ZnO nanowires integrated with metallic contacts is investigated by micro-photoluminescence measurements. Apart from surface plasmon polaritons at the air/metal interface, the emission of a single ZnO nanowire can be coupled into guided modes of surface excitonplasmon polaritons (SEPPs). The out-coupling avenues of SEPP guided modes are modeled in the presence of nanostructures, such as corrugation and gratings, on the metal surface. The guided modes of SEPPs in metalcontacted ZnO nanowires are calculated using the effective index method. The enhanced light emission from single semiconductor nanowires shows promise for use in highly efficient nano-emitters and nano-lasers, as well as macroscopic solid state light sources with very high efficiency. This article is published with open access at Springerlink.com     

Structure and microstructure of In4Te3 nanopowders prepared by solid state reaction

In this paper, we investigated the structure and microstructure of In₄Te₃ nanopowders obtained by mechanically alloying an In₇₅Te₂₅ powder mixture. Structural, chemical, thermal and vibrational studies of the In₇₅Te₂₅ powder mixture were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The orthorhombic In₄Te₃ phase (In₃Se₄-type) was nucleated in 2 h of synthesis, although non-reacted tetragonal indium (In) was still present at that time. Small amounts of cubic In₂O₃ phase were observed after 31 h of synthesis. Rietveld analyses allowed the measurement of mean crystallites sizes and phase fraction variations when milling times were increased. These analyses showed that, after 31 h of synthesis, about 65 wt% of In₄Te₃ phase contained mean crystallite sizes smaller than 27 nm and microstrains greater than 1.5%. The crystallite and interfacial components sizes were determined by high resolution transmission electron microscopy. Differential scanning calorimetry measurements showed the influence of nanometric crystallite sizes on the melting of the In₄Te₃ and non-reacted In phases. Raman measurements showed that the trigonal Te and α-TeO₂ modes, observed for the precursor Te powder, are absent for the sample milled for 31 h. The structural stability of the nanocrystalline phases of the In₇₅Te₂₅ sample milled for 31 h was attested by X-ray diffraction measurements performed twelve months after its production.     

Controlled release of ziprasidone solid dispersion systems from osmotic pump tablets with enhanced bioavailability in the fasted state

Objective: The purpose of this work was to develop a controlled release of ziprasidone with no food effect by the osmotic release strategy.

Methods: The solution of ziprasidone and poloxamer188 (P188) with different weight ratios was spray-dried to form solid dispersion of ziprasidone (SD-ZIP). The SD-ZIP was characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray powder diffraction (X-RD) and solubility testing. The SD-ZIP osmotic pump tablets were prepared by wet granulation method. The effect of formulation variables on the release characteristic was investigated. The SD-ZIP osmotic pump tablets were administered to fasted and fed beagle dogs and their pharmacokinetics were compared to commercial formulation Zeldox® as a control.

Results: The results of DSC and X-RD indicated that ziprasidone resides in P188 with no crystalline changes. Solubility studies demonstrated that the solubility of SD-ZIP was substantially improved compared to ziprasidone and physical mixtures of ziprasidone and P188. The optimized formulation and drug release profiles of SD-ZIP osmotic pump tablets in different medium were obtained which showed typical osmotically controlled release and could fitted to zero-order kinetics with good linear correlation. Pharmacokinetic studies in beagle dogs showed ziprasidone with prolong actions and no food effect was achieved simultaneously in SD-ZIP osmotic pump tablet compared with Zeldox®.

Conclusion: The SD-ZIP osmotic pump tablet could be able to enhance the bioavailability in the fasted state and showed sustained release with prolonged actions.     

Solid-state transformation in nanocrystalline Ti induced by ball milling

In the current study, we report for the first time a new Ti rhombohedral (trigonal) structure induced by HEBM and subsequent sintering. During ball milling of Ti powder, solid-state transformation does not only depend on the grain refinement but also on the successful deformation of the nano-sized crystallites due to high energy ball impacts. Thermal stability of Ti-nanocrystalline in FCC allotrope was investigated. Upon sintering, the unstable FCC restored back to the rhombohedral phase rather than to HCP. The appearance of HCP Ti after sintering could suggest that prolonged milling leads to dispersion of hard particles (HCP) into more ductile particles belonging to allotropic phases, and hence possibility of resurfacing on sintering.     

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) over a wide range of experimental parameters. The effects of the microwave power, CH₄/H₂ ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH₄/H₂ levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However, diamond film is deteriorated at high CH₄/H₂ ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH₄ concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N₂ or Ar, which is different from other reports. This composite structure has an excellent measured sheet resistance of 10–100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission (EFE) properties with a low turn-on field of 2.17 V/μm and β = 3160, therefore it could be a promising alternative in field emission applications.     

On the stress state at the yield point in symmetric bicrystals in (110) channel die compression

The stress state at the yield point in symmetric fcc bicrystals is analytically investigated for a range of crystal lattice orientations in (110) channel die compression. Although strain-rates and lattice-rotation rates necessarily are nonuniform, it is proved that the stress field satisfying both equilibrium and yield-locus constraints must lie on an edge of the locus and is thereby uniform.     

Electronic state of carbon in nanostructured composites produced by co-carbonization of aromatic heavy oil and ferrocene

The electronic state of carbon in the products of co-carbonization of an aromatic heavy oil and ferrocene in an autoclave has been studied by X-ray emission spectroscopy. Analysis of the C Kα-spectra revealed that the proportion of graphite-like component in the samples containing ferric spherical and tubular nanoparticles is about 55% and 65%, respectively. An average size of graphitic sheets forming the coating on metallic cores and the carbon matrix was estimated by the results of quantum-chemical calculations on graphene fragments to be ∼2 nm. The field electron emission properties of the studied carbon materials were found to be dependent on the graphitization degree, not on the aspect ratio of constituting nanoparticles.     

带状线法测试辐射骚扰的方法浅析

针对常规天线法辐射骚扰测量中,接收天线的位置和被测件不同极化方向影响测试结果的问题,采用带状线法进行辐射骚扰测试的方法,使辐射骚扰的测试过程更为简单便捷。     

Study of omeprazole-gamma-cyclodextrin complexation in the solid state

The possibility of obtaining inclusion complexes between omeprazole (OME) and γ-cyclodextrin (γ-CD) by kneading, spray-drying, coprecipitation, and freeze-drying was evaluated. All these methods lead to the isolation of a true inclusion compound, as evidenced by differential scanning calorimetry (DSC), infrared spectroscopy, and X-ray diffractometry on powder (PXRD). Moreover, PXRD and scanning electron microscopy (SEM) afforded data concerning crystallinity and surface characteristics of the solid phases obtained. In all cases, a significant increase of the release rate with respect to the drug alone was found, and it was attributed to the formation of an inclusion compound. Among the solid phases obtained, the coprecipitated product presented the highest dissolution rate.     

纳米碳纤维复合材料断裂电发射试验研究

采用超声波分散的方法制备了纳米碳纤维／环氧树脂复合材料，研究了纳米碳纤维／环氧树脂复合材料在拉伸和弯曲破坏时的电发射现象，并对其电发射机理进行了探讨。研究结果表明：纳米碳纤维／环氧树脂复合材料在受荷开裂和裂纹扩展过程中均存在明显的电发射现象，这一特性将为复合材料结构的在线监测及非损伤诊断提供新的方法和途径。     

Thermal annealing effects on the interface state density of metal-oxide-semiconductor capacitors with electron cyclotron resonance plasma enhanced chemical vapor deposition Silicon dioxide

Silicon dioxide films (SiO₂), deposited at room temperature by electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O₂, SiH₄ and He, present excellent structural and electrical properties. However, when fabricating field effect devices it is also crucial to minimize the defect density at the semiconductor/insulator interface. We show that the interface state density, investigated in Al/SiO₂/Si MOS capacitors, can be substantially reduced performing post-deposition annealing. In particular we studied the effects of annealing temperature and time in different gas ambient: vacuum, nitrogen and forming gas (5% H₂ + N₂). We found that interface state passivation mainly occurs when thermal annealing is performed after Al-contact deposition and that it is quite insensitive to the annealing atmosphere. The present results clearly suggest that the hydrogen passivation mechanism is driven by the H-containing species present in the film and a possible mechanism to explain the results is proposed.     

Identification of signals in the context of acoustic emission in concrete

The study presented in this paper is placed in the context of the frequency analysis of acoustic emission in concrete. The purpose is to study the ability to identify an acoustic emission event by deducing its spectrum from a detected signal. The identification is carried out progressively so as to separate the various functions involved in the acoustic emission process, and to approach the usual conditions of acoustic emission processing during fracture tests of concrete specimens. Impulses of different forms are generated on the surface of concrete test specimens, and the signals detected are analyzed. The identification of signals takes into account the frequency response of the transducers and the wave attenuation as function of the frequency.     

First-principles calculations of the structural,electronic and elastic properties of ZnWO4 and CdWO4 single crystals at the ambient and elevated pressure

Two technologically important tungstate crystals – CdWO₄ and ZnWO₄ – are studied theoretically using the plane wave based first-principles calculations. The optimized crystal structures were used to calculate the structural, electronic and elastic properties of both materials under varying hydrostatic pressure. It was shown that the band gaps, which are direct at ambient pressure, turn into indirect ones in both compounds in the pressure range from 5 to 10 GPa, whereas the values of the band gaps themselves depend only slightly on the applied pressure. Differences in compressibility along the crystallographic axes and the W–O, Cd–O, Zn–O chemical bonds were revealed and quantified by calculating the pressure coefficients for all these characteristic distances. The first estimations of the complete elastic tensor constants for both materials are reported.