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Resonant fluorescence of molecular hydrogen has been observed in the reflection nebula IC 63 with the IUE satellite. Both the noncoherent resonant scattering and the dissociative continuum are shown to agree well with molecular theory. Extended red emission is also found in this nebula and may be physically related to the dissociation of H2.
The feasibility of AES as a remote-sensing technique to map the composition of the sunlit surfaces of planetary bodies without atmospheres is studied. Solar X-rays eject photoelectrons from the planetary surface. The resulting ions relax by emission of fluorescence X-rays or Auger electrons, with energies characteristic of the element which is ionized. The spectrum of Auger electrons and photoelectrons is computed for a variety of elements and for representative lunar rock types illuminated by soft-X-ray line and continuum emission typical of solar long-lived coronal active regions. The Auger electron lines for O, Si, Mg, Al, Fe, and Ca in lunar rocks stand well above the continuum background from photoelectrons and backscattered interplanetary electrons, with typical line-to-continuum ratios from about 20 to over 1000.
Recent current density measurements with a low-beta electron beam (β=0.5-0.75) are strongly affected by electron scatter and Cherenkov limits. These invasive measurements are heavily influenced by the electron energy and the intercepting material properties: density, index of refraction, and atomic number. We evaluate various measurement methods, including x-ray scintillation and Cherenkov emission. To optimize the x-ray scintillation technique for this energy regime, metal foils of differing atomic number (Z) and thickness were placed upstream of a scintillation screen. We have selected Cherenkov emitters, based on a material refractive index, in order to differentiate the contributions from electron scatter and produced fluorescence, Cherenkov emission, and total internal reflection. The observed distributions for both approaches are verified through MCNP6®. Additionally, the simulations provide insight as to what physical processes dominate the measured distribution. We conclude by determining the limits and optimal measurement range for each measurement technique.
Long-exposure IUE observations are used here to determine the spatial distribution of the fluorescent H2 line emission in the low-excitation objects HH 43 and HH 47. In HH 43, the spatial distribution of the fluorescent H2 line emission has a width equal to or smaller than the width of the point-spread function of IUE, while both the short-wavelength UV continuum and the optical forbidden S II lines show distributions which are wider by more than a factor of two. In HH 47, the results are qualitatively analogous, but the differences between the fluorescent HH 23 emission distribution on the one hand, and the UV continuum and optical forbidden S II distribution on the other, are smaller. These distributions indicate that the appropriate conditions for the formation of fluorscent H2 lines are fulfilled only in rather narrow regions for these low-excitation objects. A continuous energy distribution in HH 43 and HH 47 is found which differs only slightly from that in the high-excitation objects HH 1 and HH 2.
Carbon dots have attracted widespread interest for sensing applications based on their low cost, ease of synthesis, and robust optical properties. We investigate structure–function evolution on multiemitter fluorescence patterns for model carbon-nitride dots (CNDs) and their implications on trace-level sensing. Hydrothermally synthesized CNDs with different reaction times were used to determine how specific functionalities and their corresponding fluorescence signatures respond upon the addition of trace-level analytes. Archetype explosives molecules were chosen as a testbed due to similarities in substituent groups or inductive properties (i.e., electron withdrawing), and solution-based assays were performed using ratiometric fluorescence excitation–emission mapping (EEM). Analyte-specific quenching and enhancement responses were observed in EEM landscapes that varied with the CND reaction time. We then used self-organizing map models to examine EEM feature clustering with specific analytes. Finally, the results reveal that interactions between carbon-nitride frameworks and molecular-like species dictate response characteristics that may be harnessed to tailor sensor development for specific applications.
Here, this study reports the synthesis and characterization of the first fluorinated coinage metal pyrazolates with SF 5 groups, specifically {[3-(SF 5 )Pz]M} 3 (M = Cu, Ag), and compares them to trifluoromethylated analogs. X-ray analysis reveals different pyrazolyl ligand orientations and metallophilic interactions, as well as supramolecular structures influenced by fluorinated substituents and metals. The {[3-(SF 5 )Pz]M} 3 complexes form face-to-face sandwich adducts with benzene. Photophysical investigations show that copper complexes exhibit long-lived phosphorescence, while silver analogs display fast fluorescence, with emission properties modulated by substituents, solvent environment, and intermolecular interactions. Computational studies confirm the experimental geometries and demonstrate that SF 5 substituents increase the π-acidity and enhance arene binding over the analogs featuring the smaller and less-electron-withdrawing CF 3 groups and provide insights into metallophilic interactions and photoluminescence. These newly uncovered SF 5 decorated materials, with enhanced π-acidity and arene-binding ability, are promising materials for molecular sensing and tunable luminescence.
Encapsulating Cs 4 PbBr 6 quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated Cs 4 PbBr 6 ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from Cs 4 PbBr 6 pseudo-spherical quantum dots is quenched and is dominated with Pb 2+ ion/silicene emission, which is very stable during the whole measurement period. For a high concentration of Cs 4 PbBr 6 ellipsoidal nanocrystals in silicon nano-sheets, we have observed Förster resonance energy transfer with up to 87% efficiency through the oscillation of two PL peaks when UV excitation switches between on and off, using recorded video and PL lifetime measurements. In an area of a non-uniform sample containing both ellipsoidal nanocrystals and pseudo-spherical quantum dots, where Pb 2+ ion/silicene emissions, broadband emissions from quantum dots, and bandgap edge emissions (515 nm) appear, the 515 nm peak intensity increases five times over 30 min of UV excitation, probably due to a photon recycling effect. This irradiated sample has been stable for one year of ambient storage. Cs 4 PbBr 6 quantum dots encapsulated in silicon nano-sheets can lead to applications of halide perovskite light emitting diodes (PeLEDs) and integration with traditional semiconductor materials.
Windowless tube spectrometer for x-ray fluorescent analysis of light elements down through fluorine
Temperature dependence of linewidths and positions of optical transitions of trivalent praseodymium doped lanthanum fluoride
Calculations of midday dayglow intensities arising from fluorescence of solar ionizing radiation
Vacuum UV determination of stability of fluorescence of sodium salicylate
Radio interference from Saturn V launch vehicle fluorescent work lamps
Organic phosphate compound synthesis, purification and use in detection of enzymatic activity in soils by fluorescence after biological oxidation
Detection of high altitude explosions based on observation of fluorescence radiation of excited nitrogen molecule or nitrogen ion from ground and from satellites
Organic sensitizers for evaluation of transition metal fluorescence in optical laser application
Fluorescent photography of droplets in spray using Q-switched laser as light source
Inhibitory effect of light from cool white fluorescent lamps on growth of yeast, alga and protozoa
Optical fluorescence, thermally tunable over significant portion of visible and near IR SPECTRUM, from phase-matched parametric system