With the aim to study and understand the optical properties of GQD materials, we performed the bottom-up synthesis of different families of nanoparticles exhibiting controlled shapes and edges. Using absorption, steady-state and time-resolved photoluminescence and photoluminescence excitation (PLE) spectroscopy, we try to establish the intrinsic optical properties of the GQDs and understand how the structure influences the properties. Here we present the synthesis of a new series of rod-shaped graphene nanoparticles (GNRods); we also present the single photon emissionproperties of a triangle-shaped GQD (Figure 1). References
CDCl 3 ] (δ, ppm): 144.51 (dq, J B-Fa = 28 Hz, J F-F = 104 Hz), 145.26
(dq, J B-Fb = 28 Hz, J F-F = 104 Hz).
All calculations were carried out taking hexane as solvent, trying to match or correlate experimental observations in a solvent with good emissionproperties and discarding toluene to avoid possible π-stacking interactions with the studied species. Geometry optimizations were carried out through all-electron calculations using the B3LYP hybrid functional at the def2SVP theory level using the SMD solvation approach, to obtain the geometries of lowest energy for the studied species and to analyze important structural details.
Table 2: TD-DFT computed UV-vis in solution (MeOH) of Cu-1. Computed oscillator
strengths are given in square brackets.
Depending on the complex, the presence of uncoordinated solvent molecules in the crystal structure led to mechano- sensitive species. While Cu-1, Cu-3 and Cu-4 (Figure S7) are relatively stable in powder form compared to their crystal forms without any changes in their emissionproperties at room temperature, complex Cu-2 loses after several minutes its emissivity upon grinding with a red shift of its emission (Figure S3, S4). Elemental analysis of room temperature vacuum dried
face or defect states related to Ga 2 O 3 -nc兲. For all tempera-
tures, these carriers recombine radiatively giving rise to a complex emission band centered at 500–550 nm. However, when the temperature increases 共above corresponding energy of 40 meV兲, the recombination states become thermally de- populated to: 共i兲 conduction band, 共ii兲 over the potential bar- rier directly to Nd +3 ions in CT process, or 共iii兲 over the potential barrier to the other defects energy levels which are in close spatial vicinity of Ga 2 O 3 -nc. However, based on the fact that observed Nd emission is characteristic of +3 oxida- tion state and direct CT from GE related donor levels to Nd requires also CT of hole to keep Nd ions optically active, we believe that the main excitation mechanism of Nd ions can be explained by two steps process via defects states. Thus, in the first step, absorbed by Ga 2 O 3 matrix carriers are ther-
In typical borondifluoride β -diketonate structures, the introduction of one or more electron donor organic fragments (D) connected by a π-conjugated segment to the acceptor dioxaborine moiety (A) leads to the generation of push-pull D-π-A or quadrupolar-like D-π- A-π-D molecules. As a consequence, the lowest-energy absorption and emission bands display a significant intramolecular charge transfer (CT) character 16,21 which allows a fine tuning of the optical properties, depending on the strength of the donor group, e.g., the absorption and emission maxima are redshifted when strong pushing groups are used 22 . In addition, a wide gap between absorption and emission maxima, that is a large Stokes shift, is desired for many practical applications, as it allows to reduce losses arising from self- absorption 23 . Among the different strategies used to induce both bathochromic shifts and enhanced Stokes shifts, the incorporation of electron donor groups 24-26 and the extension of the π-conjugation path 27-29 have proven to be particularly effective.
(transition between the lowest levels of the 4 I 13/2 and 4 I 15/2 manifolds). It is then possible to
identify different sites. A narrow line infrared laser at wavelength resonant with the first stark component of the electronic transition around 1.53µm was used.
Decay curves of the low-energy emission band (around 1540 nm) were recorded under two different excitation wavelengths: 980 and 1536 nm. The sample was a >4-mm long parallelepiped extracted from a preform, containing a cylindrical Er-doped core surrounded by pure silica. The pump beam was modulated in time with a 1-ms “square shape”. It was directed into the core along its longitudinal axis. The emitted light was collected transversally from two different points relative to the coupled pump: 1) close to the excitation point and 2) at 4 mm far from this point. The fluorescence decay signals were collected with a infrared sensitive photomultiplier Hamamatsu R 5509 (response time of the system: 100 µs) and displayed on an oscilloscope.
electrical injection . Moreover, this matrix should have much higher RE ions solubility in comparison to its silicon oxide counterpart and then allow to prevent RE clustering ions . Furthermore, Si rich silicon nitride (SRSN) has been investigated since Si excess can form clusters which act as luminescence centers to enhance RE emission . In contrast to this, various studies mention the role played by the localized states in the band tails of the amorphous matrix acting as sensitizers for RE emission [16, 20-22]. As underlined by Yerci et al., the addition of N atoms introduces more disorder than in the case of SRSO matrix. In this case, by contrast with the Si excess, the N excess (N ex ) would introduce many defects leading to the
CdSe/ZnSe quantum dots (QDs) have attracted much in- terest due to their possible application in optoelectronics. 1 In the 90s, the basic application for CdSe/ZnSe QDs was con- nected to short wave emitters and manufacturing of QDs laser. Recently, CdSe QDs have gained more interest as sources of single photon operating at room temperature. 2 II–VI self-assembled QDs such as CdSe/ZnSe are promising system for single-photon emission in the blue–green range. 3 The optical properties of QDs systems depend on many pa- rameters such as morphology, chemical composition, and chemical environment. 4 In contrast to III-V materials like InAs/GaAs, the formation of CdSe QDs differs significantly from the Stransky-Krastanov growth mode 5 so that inter- diffusion and/or segregation phenomena based on Cd-Zn exchange 6 , 7 may take place in the QD formation mechanism. In order to obtain specific properties, comprehensive nanoscale information about the dots and their surroundings are required. However, the chemical analysis of embedded QDs is challenging. Transmission electron microscopy (TEM) can give first estimation of the degree of intermixing between CdSe and ZnSe layers. The key strength of TEM is that it can directly visualize the atomic structure of a mate- rial, and a recent approach has aimed at analyzing the CdSe QDs composition using the change in lattice parameters in high resolution TEM (HRTEM) images. 8 , 9 This is an indirect method to derive information about composition. On the other hand, the strength of Atom Probe Tomography (APT) is its ability to give directly information about the 3D com- position of all chemical elements at atomic scale. 10 Thus, APT has been used recently to investigate the composition of III-V QDs, 11 II-VI layers, and II-VI/III-V interface at atomic scale. 12
separated by a small gap, radiative heat transfer surpasses that predicted by classical formulas, due to the coupling of evanescent modes on the surface of each body [1, 2]. Heat transfer is enhanced in this case, and can even be dominated by transfer through modes at specific frequencies, especially when the materials exhibit resonances such as surface phonon or surface plasmon polaritons [3–6]. Moreover, micro or nanostructured surfaces, such as periodic gratings, can scatter the thermaly excited evanescent waves into the far field, which substantially changes the emissionproperties. This mechanism has paved the way towards the design and fabrication of coherent thermal sources exhibiting both temporal and spatial coherence . Another way to couple the near field and the far field is to use the tip of a Scanning Near-Field Optical Microscopy and bring it at a submicron distance from the heated surface. The thermally populated evanescent modes can be coupled to a detector in the far field by scattering at the tip. This process underlies the principle of Thermal Radiation Scanning Tunneling Microscopy [8–10] (TRSTM), an imaging technique among others  that uses thermal radiation to perform imaging and spectroscopy of subwavelength structures.
developments have remained focused on the spontaneous emission of conventional scalar
modes into controlled directions of space, even if it is worth noting that the light thus produced
can be subsequently converted into more complex beams using far-field optical elements .
In this article, we go a step further and show how to make an assembly of colloidal quantum
and 1 for R to be preferred. An even higher gap between the two scenarios seems extremely unlikely, except for the very long term, but in the latter case it is possible to change the policy instruments and targets across time. For example, if we take the six greenhouse gas “marker scenarios” elaborated for the Special report on emission scenarios (SRES) of the IPCC (2000), the gap between the highest (A1FI) and the lowest (B2) emission scenarios reaches two only in 2050.
long-term emission trajectories defined by absolute limits would be encountered with a schedule of maximum allowed emission intensity of GDP, except for one: the economic position of countries in the distant future. If the reluctance to accept an initial cap or to negotiate more than one step at a time in the Kyoto context reflects an unwillingness to agree to an absolute cap that might require more abatement effort in the future than a nation is currently willing to accept, a growth-indexed cap would solve this problem by automatically adjusting the cap upwards (or downwards) depending on the evolution of GDP. A nation could commit to limit and reduce GHG intensity by some amount, regardless of future GDP, instead of committing to an absolute level of future emissions that might be harder or easier to achieve than expected because of variations from expected GDP. And, of course, the choice is not restricted to these two limiting cases since they can be combined to whatever extent desired or appropriate.
E-mail: firstname.lastname@example.org, Jose-Maria.Pozo@obspm.fr
Abstract. This paper introduces some general properties of the gravitational metric and the natural basis of vectors and covectors in 4-dimensional emission coordinates. Emission coordinates are a class of space-time coordinates defined and generated by 4 emitters (satellites) broadcasting their proper time by means of electromagnetic signals. They are a constitutive ingredient of the simplest conceivable relativistic positioning systems. Their study is aimed to develop a theory of these positioning systems, based on the framework and concepts of general relativity, as opposed to introducing ‘relativistic effects’ in a classical framework. In particular, we characterize the causal character of the coordinate vectors, covectors and 2-planes, which are of an unusual type. We obtain the inequality conditions for the contravariant metric to be Lorentzian, and the non-trivial and unexpected identities satisfied by the angles formed by each pair of natural vectors. We also prove that the metric can be naturally split in such a way that there appear 2 parameters (scalar functions) dependent exclusively on the trajectory of the emitters, hence independent of the time broadcast, and 4 parameters, one for each emitter, scaling linearly with the time broadcast by the corresponding satellite, hence independent of the others.
Genova, Italy, 9 Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland, 10 Department of Piston
Machines and Internal Combustion Engines, University of Rostock, Rostock, Germany, 11 Aerosol d.o.o., Ljubljana, Slovenia, 12 Now at Condensed Matter Physics Department, Jožef Stefan Institute, Ljubljana, Slovenia
Abstract We characterized the chemical composition and optical properties of particulate matter (PM) emitted by a marine diesel engine operated on heavy fuel oil (HFO), marine gas oil (MGO), and diesel fuel (DF). For all three fuels, ∼80% of submicron PM was organic (and sulfate, for HFO at higher engine loads). Emission factors varied only slightly with engine load. Refractory black carbon (rBC) particles were not thickly coated for any fuel; rBC was therefore externally mixed from organic and sulfate PM. For MGO and DF PM, rBC particles were lognormally distributed in size (mode at d rBC ≈120 nm). For HFO, much larger rBC
Variations in both flux and spectral shape are thus detected for three stars, as well as for θ 1 Ori C (Gagn´e et al. 2005; Stelzer et al. 2005). Moreover, for HD 191612, θ 1 Ori C, and possibly Tr16-22 12 , the flux variations are clearly phased with the stellar rotation period, as demonstrated by the simultaneous minima in X-ray and optical emissions. This can be qualita- tively explained in the case of magnetic oblique ro- tators: as the view on the magnetosphere changes as the star rotates, occultation of the X-ray emitting re- gions by the star or obscuration by its confined wind can cause periodic variations, recurring with the stel- lar rotation period. However, the latter explanation can be discarded: a large increase in absorption would be required to explain the observed flux decreases, but no significant one (i.e. larger than 2–3σ) was detected during our spectral fitting nor for θ 1 Ori C, (Gagn´e et al. 2005, see in particular their Fig. 14). Moreover, if absorption was the cause of the flux vari- ations, the X-ray emission would actually always be softer when the flux is minimum, which is not the case (see below).
Title : Plasma X-ray emission : spectroscopy and high-resolution imaging
Keywords : Atomic physics, laser-matter interaction, X-ray spectroscopy, instrumentation, Fresnel zone plate, X-ray imaging, inertial confinement fusion
Abstract : Most of plasmas created in laboratories for experiments in domains such as inertial confinement fusion are non-LTE plasmas. The modeling of the atomic kinetics of these plasmas is crucial to understand the radiative properties of these environments. There is a strong demand for experiments in which the plasma is characterized by independent X-ray spectroscopy diagnostics. Thus the development of new diagnostics for these experiments is also a major stake.