White light emission from a single component system: remarkable concentration effects on the fluorescence of 1,3-diaroylmethanatoboron difluoride

Concentration effects on the fluorescence (FL) emission of 1,3-dibenzoylmethanatoboron difluoride (1aBF₂) and its diisopropyl derivative (1bBF₂) in KBr and CH₂Cl₂ were investigated. Powder samples of 1aBF₂ and 1bBF₂ in KBr exhibit yellow and white FL emissions, respectively, whose intensities and wavelengths are not significantly affected by concentration. In contrast, remarkable concentration effects on FL properties of these compounds in CH₂Cl₂ solutions were observed. Increases in the concentrations of 1aBF₂ and 1bBF₂ from 1 × 10⁻⁷ to ca. 2 × 10⁻¹ M lead to dramatic changes in the FL colors from blue (398 and 411 nm, respectively) to yellow (548 and 558 nm) via white. Careful analysis of the FL spectra, involving lifetime determinations and wave deconvolutions, reveals that emissions from 1BF₂ involve two FL domains, corresponding to an excited monomer and an excimer, and that concentration increases promote a continuous change from the former to the latter major FL domain. Thus, white FL of 1aBF₂ and 1bBF₂ is achieved by modulation of the dual FL of the excited monomer (blue) and excimer (yellow). These findings indicate that 1,3-diaroylmethanatoboron difluoride (1BF₂) represents a new white emitting material that has advantageous features which arise from the fact that it is an easily prepared, low molecular weight, single component system not containing a heavy metal atom.     

Transient EPR emission spectra of a free radical trapped in a single crystal of chloranil

The EPR spectrum of a free trapped in single crystals of chloranil changes its phase from absorption to emission when the crystal is illuminated by visible light. The time evolution of the EPR signal is discussed in terms of the interaction between the doublet species and triplet excitons produced by light excitation.     

Unusual emission properties of a triphenylene-based organogel system

We have found that compound 1 forms organogels in appropriate organic solvents and the resultant gel phase exhibits unusual emission properties arising from the excimer formation.     

Triplet xanthone in n-pentane: multiple emission from a single site

The three phosphorescence components of xanthone in n-pentane originate from three states of one solvated species: From the z sublevel of the second triplet state, of ³nπ^* origin, and from two widely split sublevels of the lowest triplet state, of ³ππ_* origin. Its z sublevel is thermally depleted across the spin-orbit mixing induced zero-field sublevel splitting of 15.1 cm^?1.     

Electron field emission characteristics and field evaporation of a single carbon nanotube

Direct transmission electron microscope (TEM) observations of the field emission and evaporation process of emitting carbon nanotubes (CNTs) shown that the tip structure of the CNT is in general composed of irregular shaped graphitic sheets which extend typically more than 10 nm from the end of the CNT. It is found that the irregular shaped graphitic sheets at the tip of the CNT may greatly enhance the field emission characteristics of the CNT when compared with that having an ideal circular edge. The field evaporation of the CNT proceeds typically via the removal of the irregular shaped graphitic sheets from the tip of the CNT, and field emission characteristics of a CNT depend far more sensitively on the tip structure than on the geometric length of the CNT.     

Secondary emission of doped lithium hydride single crystals

Experimental studies of resonance Raman scattering (RRS) and of luminescence of excitons interacting with an impurity field and phonons in lithium hydride (LiH) crystals doped with Al, Mg, and Zn have been made. It has been shown that the presence of doped metal ions modifies the relaxation processes of excitons in the LiH lattice and gives rise to bound excitons with large and small radii.     

Spectroscopic measurements of single atom emission in an optical resonator

Experiments are described in which atoms are placed in a concentric optical resonator and probed by cw dye laser radiation. It is found that, depending on the tuning of the resonator, the radiative linewidth of the atomic transition may either increase or decrease and the observed resonance frequency may shift, relative to their respective free space values. A simple classical interpretation of these effects is given. We also present results of a semi-classical calculation which show that under appropriate conditions, stimulated emission may play a significant role in such experiments.     

Solvation emission spectral peaks of single molecular oxygen

Distinct new emission peaks of solvated single (¹Δ_g) molecular oxygen, generated by photosensitization, are observed in a series of oxygen-sa     

Enhanced white-light emission from multiple fluorophores encapsulated in a single layer of diblock copolymer micelles

Enhanced white-light emission was achieved by loading green- and red-light-emitting donor-acceptor pairs in the separate micellar cores and blue-light-emitting polymers around their periphery. Fluorescence resonance energy transfer was enabled between a donor and an acceptor in cores, but was suppressed among these three light-emitting species by micellar coronas, which resulted in their enhanced simultaneous emissions.     

Experimental considerations of myocardial single photon emission CT image with a cardiac phantom

We studied the quantity of thallium-201 myocardial single photon emission CT (SPECT) image with a cardiac phantom. The myocardial SPECT image is influenced by several causes, i.e., the absorption of gamma rays, collimator aperture, statistical noise and limited angle of rotation in data acquisition. The attenuation correction under the assumption of uniform distribution is not sufficient, so we have to consider the actual distribution of absorption. The effects of the nonuniform attenuation are most prominently appeared when we evaluate the quantity by the integral method. The aperture characteristics of a collimator are decided by the distance between the rotational center of the gamma camera and the collimator surface. Simultaneously scattered gamma rays affect the reconstructed image in the low frequency component, so the effective attenuation coefficient varies gradually. The statistical noise intermixed in the projection data generate artifacts like as lump-shaped pattern. The noise are clearly appeared in the spatial frequency upper than 0.25 cycle, so the low-pass filter are required with that of cut-off frequency. Moreover to enhance the details of the radionuclide distribution of cardiac muscle, the Wiener filter should be applied. The scan area also affects the appearance of the artifact in the myocardial SPECT image. The 180-degree scan usually generates false defects just nearby the center of reconstructed cross section. And the positions are changed with the conditions of gamma ray absorber and its relative position to the myocardial area. The 360-degree scan should be used from the standpoint of reconstructing more quantitative image.     

Ratiometric oxygen sensing: detection of dual-emission ratio through a single emission filter

A new method and device for the ratiometric measurement of oxygen concentration are presented. They are based on the use of a dual-emission oxygen-sensitive dye. The method allows the exclusion of the influence of emission overlap. The detection of the dual-emission ratio is performed using a single long-pass emission filter. The device described is simpler than the widely used lifetime instruments and could easily be a stand-alone low-cost instrument.     

Evaluation of the system performance and clinical images of the single photon emission computed tomography for head using ring arranged detector

To evaluate the system performance, several preoperational fundamental tests of single photon emission computed tomography (SPECT) were carried out. Spatial resolutions (FWHM) measured with the point-spread functions of a 99mTc line source were 12.5 mm with a high resolution (HR) collimator and 17.2 mm with a high sensitivity (HS) collimator respectively. Slice thicknesses (FWHM) obtained from the profile curves of slice images were 17.5 mm (HR) and 29.0 mm (HS) at the center of rotation. System sensitivities were 5.4 kcps/slice (HR) and 27.8 kcps/slice (HS). Uniformities calculated from the SPECT images of a pool phantom were 4.7% (HR) and 2.7% (HS) at the condition of 3,000 kcounts to be acquired. SPECT images of the HEADTOME SET-031 were considered very useful to diagnose the cerebrovascular disease.     

Four-level optical line shape of a single molecule coupled to a single tunneling two-level system

We propose a density-matrix theory for the four-level system consisting of a single optical two-level system (OTLS) coupled to a single two-level system tunneling along a vibrational coordinate (VTLS). Phonons induce jumping rates of the VTLS, but coherent tunneling has to be considered explicitly as well, because the Born-Oppenheimer potential of the tunnel variable may change upon optical excitation. The OTLS is subject to spontaneous emission and driven by a laser wave with arbitrary strength. Numerical simulations for various coupling cases reproduce limiting behaviors previously discussed separately in the literature, such as motional narrowing, cross transitions, optical saturation and pumping, and nonlinear effects. Our model also perfectly fits recent measurements of the spectra of a single molecule coupled to a single tunneling system in a disordered crystal.     

In vivo imaging of brain dopaminergic neurotransmission system in small animals with high-resolution single photon emission computed tomography.

High-resolution single photon emission computed tomography (SPECT) provides a unique capability to image the biodistribution of radiolabeled molecules in small laboratory animals. Thus, we applied the high-resolution SPECT to in vivo imaging of the brain dopaminergic neurotransmission system in common marmosets using two radiolabeled ligands, [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (beta-CIT) as a dopamine transporter (DAT) ligand and [123I]iodobenzamide (IBZM) as a dopamine D2 receptor (D2R) ligand. Specific images of the striatum, a region with a high density of dopaminergic synapses, were obtained at 240 min and 60 min after injection of [123I]beta-CIT and [123I]IBZM, respectively. Furthermore, a significantly low accumulation of [123I]beta-CIT in the striatum was observed in MPTP-treated animals compared with results for a control group, and a similar accumulation in the control group was observed with the pretreatment of deprenyl in the MPTP-treated animals. However, the striatal accumulation of [123I]IBZM showed no changes among the control, MPTP-treated, and deprenyl-MPTP-treated groups. These SPECT imaging results agreed well with those of DA concentration and motor behavior. Since MPTP destroys nigrostriatal dopamine nerves and produces irreversible neurodegeneration associated with Parkinsonian syndrome, SPECT imaging data in this study demonstrated that deprenyl shows its neuroprotective effect on Parkinsonism by protecting against the destruction of presynaptic dopamine neurons.     

Photon-by-photon determination of emission bursts from diffusing single chromophores

One of the difficulties in diffusion-type single-molecule experiments is the determination of signal amid photon-counting noise. A commonly used approach is to further average the noisy time trace by binning, followed by placing a threshold to discriminate signal from background. The choice of smoothing parameters and the placement of the threshold may impact on the efficiency with which the information-rich region can be harvested, among other potential complications. Here we introduce a procedure that operates on the data sequence photon by photon, thereby relieving the incertitude in choosing binning-thresholding parameters. We characterize this procedure by detecting the two-photon emission bursts from diffusing single gold nanoparticles. The results support our burst-finding procedure as a reliable and efficient way of detecting and harvesting photon bursts from diffusing experiments.     

Field emission investigation of single Fe-doped SnO2 wire

Tin oxide submicronwires doped with Fe element were prepared by the thermal evaporation method. Morphological and structural characterizations revealed wires with sub micron size and crystalline in nature. The field electron emission from the single Fe:SnO₂ wire was carried out in conventional field emission microscope. The Fowler–Nordheim plot obtained from I–V characteristics of the wire showed a linear behavior typical that of metal. The field enhancement factor estimated from the slope of the F–N plot is 7455 cm^?1, indicating that the field emission is from nanometric features of the emitter. A current density of 10 A/cm² has been obtained at an applied field of 4.845 × 10³ V/μm. The field emission current–time record at a current level of 1 μA for more than 3 h duration is promising for various field emissions based applications.     

Identification of a single light atom within a multinuclear metal cluster using valence-to-core X-ray emission spectroscopy

Iron valence-to-core Fe Kβ X-ray emission spectroscopy (V2C XES) is established as a means to identify light atoms (C, N, O) within complex multimetallic frameworks. The ability to distinguish light atoms, particularly in the presence of heavier atoms, is a well-known limitation of both crystallography and EXAFS. Using the sensitivity of V2C XES to the ionization potential of the bound ligand, energetic shifts of ~10 eV in the ligand 2s ionization energies of bound C, N, and O may be observed. As V2C XES is a high-energy X-ray method, it is readily applicable to samples in any physical form. This method thus has great potential for application to multimetallic inorganic frameworks involved in both small molecule storage and activation.