A Porphyrin Pentamer as a Bright Emitter for NIR OLEDs

The luminescence and electroluminescence of an ethyne-linked zinc(II) porphyrin pentamer have been investigated, by testing blends in two different conjugated polymer matrices, at a range of concentrations. The best results were obtained for blends with the conjugated polymer PIDT-2TPD, at a porphyrin loading of 1 wt%. This host matrix was selected because the excellent overlap between its emission spectrum and the absorption spectrum of the porphyrin oligomer leads to efficient energy transfer. Thin films of this blend exhibit intense fluorescence in the near-infrared (NIR), with a peak emission wavelength of 886 nm and a photoluminescent quantum yield (PLQY) of 27% in the solid state. Light-emitting diodes (LEDs) fabricated with this blend as the emissive layer achieve average external quantum efficiencies (EQE) of 2.0% with peak emission at 830 nm and a turn-on voltage of 1.6 V. This performance is remarkable for a singlet NIR-emitter; 93% of the photons are emitted in the NIR (λ > 700 nm), indicating that conjugated porphyrin oligomers are promising emitters for non-toxic NIR OLEDs.

Impacts of Autofluorescence on Fluorescence Based Techniques to Study Microglia

Microglia, the resident immune cells in the central nervous system, accrue autofluorescent granules inside their cytoplasm throughout their lifespan. In this report, we studied the impacts of autofluorescence on widely used fluorescence based techniques to study microglia, including flow cytometry, immunofluorescence staining and live imaging. The failed attempt of using fluorescein isothiocyanate (FITC) conjugated antibody to detect LAG3 protein in microglia prompted us to compare the sensitivity of FITC, PE and APC conjugated antibodies to detect surface protein expression in microglia. We found that phycoerythrin (PE) outperforms FITC and allophycocyanin (APC) as the fluorophore conjugated to antibody for flow cytometry by overcoming the interference from microglia autofluorescence. To identify the location and source of microglia autofluorescence, we did confocal imaging and spectral analysis of microglia autofluorescence on fixed brain tissues, revealing that microglia autofluorescence emits from cytoplasmic granules and displays a multi-peak emission spectrum. On live brain slices, autofluorescence could reduce the detected calcium signals imaged by GCaMP6s in microglia. In conclusion, autofluorescence is a critical factor to consider when designing experiments and interpreting results relying on fluorescence based techniques to study microglia.

Investigate the Double Peaks in Main Emission of UVB LEDs

In this study we suppressed the parasitic emission caused by electron overflow found in typical UVB light-emitting diodes (LEDs). Furthermore, modulation of the p-layer structure and doping profile allowed us to decrease the relaxation time of the holes to reach conditions of quasi-charge neutrality in the UVB quantum well. Our UVB LED (sample A) exhibited a clear exciton emission, with its peak near 306 nm and a band-to-band emission at 303 nm. The relative intensity of the exciton emission of sample A decreased as a result of a thermal energy effect. At temperatures of up to 363 K, sample A displayed the exciton emission. Our corresponding UVC LED (sample B) exhibited only a Gaussian peak emission at a wavelength of approximately 272 nm.

Perfecting and extending the near-infrared biological window

In vivo fluorescence imaging in the second near-infrared window (NIR-II) has been considered as a promising technique for visualizing the mammals. However, the definition of the NIR-II region and the mechanism accounting for the excellent performance still need to be perfected. Herein, we simulated bioimaging in the NIR spectral range (to 2340 nm), confirmed the positive contribution of moderate light absorption by water in intravital imaging and perfected the NIR-II window as 900-1880 nm, where the 1400-1500 nm was defined as NIR-IIx region and the 1700-1880 nm was defined as NIR-IIc region, respectively. Moreover, the 2080-2340 nm was newly proposed as the third near-infrared (NIR-III) window, which was believed to provide the best imaging quality. The wide-field fluorescence microscopy in brain, in addition, was performed around NIR-IIx region with excellent optical sectioning strength and the largest imaging depth of in vivo NIR-II fluorescence microscopy to date. We also proposed 1400 nm long-pass detection in off-peak NIR-II imaging whose profits exceeded those of NIR-IIb imaging, using bright fluorophores with short peak emission wavelength.

Hard X-ray impact on the ionosphere D-layer: new results from VLF measurements

<p>The ionospheric electron density reacts to a change of ionization condition by a time delay Δt. Appleton (1953) demonstrated that this time delay is inversely proportional to the product of the electron density Ne and recombination rate coefficient α. Thus, the evaluation of the time difference between the peak time of VLF emission, which is supposed to represent the instant of maximum ionization, and the ionization source's peak time provides an easy way to estimate α Ne. First used to evaluate the increase of electron density at noon from H α peak emission, this technic was also employed to estimate the recombination rate during solar flares. The GOES Soft X-ray emissions (i.e. in the range 1.5-12keV) are then considered to determine the ionising source peak time.</p><p>Based on VLF measurements obtained from the SUPERSID antenna installed at the Meudon site of the Paris Observatory (France), we computed each flare's time delay from January 2017. We benefit from the events of September 2017, the strongest from the last 10 years. We thus demonstrate the prominent role of Hard X-Rays in ionizing the D-layer of the ionosphere.  </p>

A data-driven approach to predicting band gap, excitation, and emission energies for Eu2+-activated phosphors

An integrated ML model platform is developed to predict the peak emission wavelength (PEW), excitation band edge wavelength (EBEW), and band gap (Eg) from structural, elemental, chemical, and physical descriptors of Eu2+-activated phosphors.

Study on the Validity of Wien’s Displacement Law on Tungsten Bulb

This work was mainly based on three interdependent parameters, which are temperature, emissivity and peak emission wavelength. Temperature is the primary parameter that determines how much light the filament gives off, and at what wavelengths. The work was focused on temperature determination of tungsten filament with different values of emissivity. The different values of emissivity taken for the work were 0.433, 0.431, 0.427, 0.421 and 0.415. Peak emission wavelength was calculated at different tungsten temperatures for different wattage bulbs which was in the order of 10-6m. 6, 60, and 500 watt bulb were taken for the work. The peak of the spectrum lay in the infrared region. Wien’s displacement law was used to calculate the value of peak emission wavelength. The work was based on theoretical model. Blackbody spectrum curve was used to analyze the emitted radiations from the bulb. In each spectrum curve, radiations having higher wavelengths were emitted in greater amount than the radiations having lower wavelength. Spectral radiance was found to be dependent upon both emissivity and power of the bulb. The area under the blackbody spectrum curve indicated the total number of emitted radiations and hence the total energy radiated across all wavelengths. The total energy emitted from tungsten filament was found to be increased rapidly with temperature. Brightness of the bulb increased with the increase in temperature of the tungsten. The peak in the blackbody spectrum curve shifts towards left, when temperature increased. There is a direct consequence of the brightness of bulb with the peak emission wavelength.

Exospheric Na distributions along the Mercury orbit with the THEMIS telescope

<p>The variability of Na exosphere of Mercury shows time scales from less than one hour to seasonal variations. While the faster variations, accounting of about 10-20% of fluctuations are probably linked to the planetary response to solar wind and Interplanetary Magnetic Field variability, the seasonal variations (up to about 80%) should be explained by complex mechanisms involving different surface release processes, loss, source and migrations of the exospheric Na atoms. Eventually, a Na annual cycle can be identified. In the past, ground-based observations and equatorial density from MESSENGER data have been analysed. In this study, for a better investigation of the exospheric Na features, we have studied the local time and latitudinal distributions of the exospheric Na column density as a function of the True Anomaly Angle (TAA) of Mercury by means of the extended dataset of images, collected from 2009 to 2013, by the THEMIS solar telescope. Our results show that the THEMIS images, in agreement with previous results, registered a strong general increase at aphelion and a dawn ward emission predominance with respect to dusk ward and subsolar region between 90° and 150° TAA. Unlikely other analyses, ours evidences a predominance of subsolar column density along the rest of Mercury’s orbit. An unexpected relationship between Northward or Southward peak emission and both TAA and local time is also evidenced by our analysis. This result seems to contradict previous results obtained from different data sets and it is not easily explained, thus it requires further investigations.</p>